Line Movement in Sports Betting: How a Price Moves From Open to Kickoff to Final Whistle

At a sportsbook a bet has two numbers. The line is the point spread or total, Chiefs -3.5 or over 47.5. The price is what a bet on either side of it costs, usually -110. When the market moves, the sportsbook usually moves the line and holds the price: Chiefs -3.5 becomes Chiefs -4 at the same -110. Sometimes it moves the price and holds the line: -3.5 at -115. A moneyline has no spread, so only its price moves, -150 to -170.

On Polymarket every market is a contract that pays $1 if a stated thing happens. The line is fixed in the market itself: there is a market for Chiefs -3.5, and if the market wants Chiefs -4 that is a different contract. What moves is the price, in cents, and the price is the probability. Chiefs -3.5 trading at 48¢ means the market thinks the Chiefs cover by four or more 48% of the time. If money comes in on the Chiefs, that contract goes to 52¢, 55¢, 58¢, and the total and moneyline markets on the same game move with it.

This matters for reading movement. At a sportsbook, a half-point of line movement is a lumpy signal that something crossed a threshold. On Polymarket, movement is continuous and in probability units, so a move from 48¢ to 55¢ is exactly a seven-point change in the market's estimate, and every trade that caused it is on a public ledger with a wallet address attached.

Money moves a line. A sportsbook that takes too much on one side moves the line to attract the other and limit its exposure, and it moves further and faster for bettors it respects than for the public. An order book moves for a simpler reason: a buyer takes the offers at 48¢ and 49¢, and the next offer is 50¢.

Information moves a line. A starting pitcher is scratched, a quarterback is listed doubtful, the lineups drop an hour before a soccer match, the weather turns. The first bettors to act on the news get the old price; the line then moves to the new one, and their edge is the distance it moved.

Time moves a line. The closer to kickoff, the more of the information is in and the more money has voted, so the price converges toward its best estimate and the spread narrows. Across 0xinsider's Polymarket sports trades, the average quoted spread on a large buy placed more than a week before kickoff was 18¢. On the day of the game it was 1.1¢. That is the difference between a price nobody has sharpened yet and a price everyone has.

And the game moves the line. Once play starts, a goal, an injury or a run of outs moves the price more in a minute than the whole pre-game week did. A sportsbook reprices in-play with a delay and a wider hold. A Polymarket market keeps trading on the same book at the same one-cent spread, and by the second hour of play a third of large buys are on a side already trading at 80¢ or more.

Steam is a sudden, sharp move in the same direction across many sportsbooks at once. It happens when a bettor or a syndicate the books respect hits the same side everywhere within minutes, and every book moves to protect itself. Chasing steam means betting the side that moved, on the theory that whoever moved it knows something. The problem is that by the time you see it, you are paying the new price.

Reverse line movement is a line that moves against the side most of the tickets are on. If 70% of bets are on the home team and the line moves toward the away team, the money on the away side is bigger and more respected than the tickets on the home side. It is the classic sign that the public and the sharp bettors disagree, and that the book is siding with the sharps.

Both are ways of inferring who is behind a move from the shape of the move, because at a sportsbook the bettors are invisible. On Polymarket they are not. Every large buy is a wallet with a settled record, and 0xinsider grades that record. The equivalent of reading reverse line movement is looking at which side the profitable wallets are on, which the sharp money strip on each sports board shows directly. The chart above is an illustrative market, not a real one: it shows the drift, the lineup jump, the sized money three hours out and the in-play swing that this guide is about.

0xinsider timed 396,830 Polymarket sports buys of $1,000 or more against kickoff, across every sport that settled between April 2 and September 11, 2026. Half of them, 48.6%, landed after the game had started. The last hour before kickoff took 22.8% and the first hour of play 22.4%, so four in ten large sports bets land in the two hours around the opening whistle. Only 12.6% landed more than six hours out, and a tenth of a percent more than a week out.

The bets grow as kickoff approaches. A week out the average large buy was $11,020. In the last hour it was $22,468. The largest average stakes, $23,496, landed more than two hours into play, on long games and second-half markets. A sportsbook sees the same curve from the other side, thin when the line opens and flooding in the hour before the game, except that the sportsbook's curve ends at kickoff and Polymarket's does not.

The study is at 0xinsider.com/research/when-large-sports-bets-land. For reading movement, the point is that most of the information a price will ever carry arrives in a narrow window around kickoff, and that a Polymarket price keeps carrying new information for two hours after a sportsbook has stopped.

The received wisdom at a sportsbook is that the closing line is the sharpest and that early lines are soft, which is why professionals bet openers. The Polymarket data agrees about the sharpness and disagrees about who benefits. Buys placed one to seven days before kickoff won 56.5% of the time at an average price of 59.7¢: minus 3.21 points, with a 95% interval from minus 5.09 to minus 1.35. Buys placed more than a week out came in at minus 5.55 points on a smaller sample.

From six hours before kickoff to the final whistle, every timing bucket was calibrated: within a point of zero, with an interval that includes it. The large buyer who waited for the day of the game paid a fair price. The large buyer who bet a week early paid an 18¢ spread on average to hit a price that had not yet absorbed the lineups, and in this sample was wrong more often than that price said.

So early lines are soft on Polymarket too, and the softness has gone to whoever was on the other side of the early money. If you have information a week out, the price is there to be taken. If you do not, the data says wait.

Line movement has a cost that is easy to forget: to bet at all you cross the spread, and the spread is part of the price. On Polymarket sports markets the quoted spread at the moment of a large buy was one cent at the median in every sport and every timing bucket from April through July 2026. The 90th percentile was one cent in soccer, the NBA, baseball and hockey and two cents in tennis, esports, MMA and the WNBA.

A taker at 50¢ crossing a one-cent book pays half a cent above the midpoint, 1% of the stake, plus Polymarket's sports taker fee of 2.5% of the stake at that price. A resting limit order pays no fee and collects the spread instead. Against a sportsbook's 4.55% hold at -110, a Polymarket taker pays about 3.5% and a maker nothing, but only on the day. A week out the mean spread was 18¢, and the guide at 0xinsider.com/learn/how-to-read-polymarket-order-book explains how to see it before you trade.

Before kickoff most large buys are near a coin flip: in the last hour before the game 55.1% of buys were between 40¢ and 60¢ and 9.5% were at 80¢ or more. In the first hour of play the 40-to-60 share falls to 35.9% and the 80-plus share rises to 21.6%. In the second hour a third of all large buys are at 80¢ or more. A team is ahead, and the money is on it.

Those live prices were fair. In-play buys at 70¢ and up paid 84.1¢ and won 84.5% of the time. In-play buys between 30¢ and 70¢ came in at plus 0.52 points. The live longshot was the one exception: buys under 30¢ during play won at their price but returned minus 10.4% on the dollar, because the stakes that lost were larger than the stakes that won. Buying the team that is behind is cheap for a reason.

Which sports trade live is a fact about the sport. Cricket buys landed in-play 89% of the time, MMA 73%, tennis 73%, esports 66%. Soccer was 36%, hockey 31%, the WNBA 27%. In every sport with both phases, the in-play price was fairer to the buyer than the pre-kickoff price. Tennis buys before the first serve came in at minus 3.21 points; tennis buys during the match at plus 0.39.

From June 2026, when 0xinsider's grade coverage widened, every large buy also carries the grade its wallet held that day. Wallets graded S, A or B placed 51.3% of their sports buys in-play. Wallets graded D or F placed 37.0% in-play and 59.0% on the day before kickoff. The well-graded wallets are half live bettors; the poorly graded wallets are pre-game bettors.

Before kickoff the grade barely separates anyone: in the last hour before the game, S, A and B wallets came in at minus 0.42 points and D and F wallets at minus 0.30. In the first hour of play, S, A and B wallets came in at plus 3.07 points and D and F wallets at minus 3.03, six points apart on the same games in the same hour. That gap is the whole of the sports grade study at 0xinsider.com/research/sharp-money-polymarket-sports.

For a bettor reading movement, this is the answer to the question steam and reverse line movement try to guess at. On Polymarket the price moves during the game because a goal or an injury changed it, and the wallets that were right about the change are, in this data, the wallets that had been right before. When the sharp money strip on a game moves during play, that is who moved it.

Each game on a 0xinsider sports board, 0xinsider.com/sports/nfl, 0xinsider.com/sports/nba, 0xinsider.com/sports/soccer, 0xinsider.com/sports/tennis and the rest, shows the moneyline, spread and total prices, the kickoff countdown, and the live score once the game starts. The sharp money strip on each game shows which side the profitable wallets are on and how much they have on it, and it updates through the game.

The whale alerts feed at 0xinsider.com/whale-alerts is the movement itself: every large buy as it lands, timestamped, with the buyer's grade beside it. Watching a game's feed in the hour before kickoff shows you the money this guide calls late; watching it in the first hour of play shows you the money that separates the grades. Alerts on a wallet or a game send the same fill to you the moment it clears.

The pick of the day at 0xinsider.com/pick-of-the-day records the entry price and the closing price for each pick, which is closing line value on the public record. The guide at 0xinsider.com/learn/closing-line-value covers the measure, and 0xinsider.com/learn/sports-betting-analytics-guide puts it beside the other numbers a bettor needs.