Chasing

1. The act of staying in the hand against a bet in the hopes of hitting a hand, usually a flush or a straight.

Explained

The term chasing is used to refer to a player that does not have a made hand and needs to hit a card to complete it. For example, players who are "chasing" are usually drawing to a flush or a straight. Typically, fish are chasing despite the correct pot odds.

Abusing Chasers

Chasers, a.k.a. fish or donkeys, are usually dead money and thus, you should always be looking for ways to get their stack. You can often use the donkey's chasing against him. For example, let's say a fish opens to 4x from the button, and it folds to you in the BB with KcKs. You decide to three-bet, and obviously the donk flats. When the flop comes down Th-6h-2s, you lead for half the pot and again, your opponent calls. The turn is the Kd, and the action goes bet-call. At this point, it's pretty clear that the fish is chasing a flush, so when the river bricks and drops the 3d, you can assume that your opponent missed their draw and has absolutely nothing. In this spot, checking to the donk is often the most optimal line, because a high percentage of the time they will bluff off the rest of their stack in a last ditch effort to justify their chasing. So, you decide to check-call your opponent's all-in, and you win a massive pot when they show up with Ah7h (a busted flush draw).