A player on a chase keeps betting to recover money they have already lost. It happens in casino games and sports betting alike, and it usually comes with bigger, faster and less considered bets than the player would normally make.
Chasing rests on a false idea: that a loss is a debt the game will repay. Results are independent, so the next bet is no more likely to win because the last one lost. Systems that raise the stake after every loss, such as the Martingale system, can drain a bankroll quickly. Closely related ideas include steaming and the end-of-the-day betting effect.
Loss chasing is also widely treated as a warning sign of problem gambling. For operators, that makes it a key behaviour to monitor: sudden stake increases, rapid re-deposits after losses and reversed withdrawals can prompt responsible gambling contact, deposit limits or cooling-off periods.