Definition
A 'hot game' is one in which professional sports gamblers, and the like (sharps), are all on one side. Often the sportsbooks catch wind of this and adjust their line accordingly.
Signs of a 'hot game
'
When the oddsmakers release a line that is 'soft', professional sports gamblers and sharps often pounce on such a line. This influx of money often moves the line, but not as one would expect. There are some signs that one can recognize in identifying a 'hot game', they are listed below for easy reference:
In the National Football League-since lines come out a week before the actual game, lines that move early (opening line) are often sharp money plays
In general, if a line moves in one direction but the money is being poured on the other side, then the 'correct' play is the side that is being bet less (also known as a contrarian play and reverse line movement play).
In lesser-known matchups (not high profile games), if the line moves several points, then the side that is being bet on is usually the sharp play. For example if team A (a small school in an unknown conference) opens up at -3, then is bet up to -6, then such a side is almost always sharp.
What's the difference between a 'hot game' and a heavy handle game?
The main difference between a 'hot game' and a heavy handle game is simple: although both types of games involve heavy action, only the 'hot game' involves sharp money. Heavy handle games usually are the result of heightened public interest, such as high profile games, games on national television, and/or the only game for the day (ie. Monday Night Football). Sportsbooks love these types of games, for if the action is pretty well balanced, then no matter which side wins, the sportsbooks win on vigorish.
Sportsbooks fear a 'hot game'
As stated above, 'hot games' are those in which smart money is involved. Sportsbooks fear such a game because they know if action is not balanced, they will lose. Such is the reason why they adjust their lines accordingly and attempt to dupe the public into taking the wrong side. This reverse line movement is most evident in college football (NCAAF) and the National Basketball Association (NBA). As stated above, if the line moves in one direction, but most of the money is on the other side, then the 'correct' play is the side that is receiving less action.
Summary
A 'hot game' is one in which professional and sharp money players are all on one side. Sportsbooks fear such a game the most, since they know if action is not balanced, they will lose.