Hustling is the act of grifting a mark for money in a game. The mark is targeted as having significantly less skill than the hustler. The hustler will then prey on the marks confidence in order to trick them into betting on their ability to win. This is typically something that happens in pool halls, but has become wide spread across most sports.
The Hustler will gain the confidence of the mark by playing a few casual games winning and losing where appropriate. When the Hustler believes he or she has the confidence of the mark he will put a small wager on the match IE $20. Typically the hustler will throw that game, and then bet an astronomically higher amount on the second game. A good hustler will let you win two or three times slowly upping the betting amount until he or she appears to be incredibly frustrated and puts up a bet that is too good to be true.
Ex of Hustling:
Hustler: Shit I lost again, man your good. I got 20 bucks that says you can't win the next game.
The Mark: Your on.
In the Long Con the Hustler would attempt to drag this out for a couple of games building the dollar amount by 10 or 20 at a time. This would really build the confidence of the mark so that when the hustler actually puts up a thousand dollar game the mark is very confident that they will beat them.