"Sandbagger" is a derogatory term in golf that applies to golfers who cheat by pretending to be worse golfers than they really are. The term can be thought of two ways:
1. Generally, any golfer who misleads others about his ability level, claiming to be worse than he actually is at golf, might be a sandbagger. If the person is not trying to gain from that deception, no problem (he might even be aware he is misleading others about his ability - he might just have low self-esteem). But a golfer who deliberately misleads others about his ability in order to gain in some way - to win a bet, for example - is a sandbagger.
2. More specifically, a sandbagger is a golfer who artificially inflates his handicap index in order to better his chances of winning tournaments or bets.
A sandbagger is considered by many to be the lowest form of life on a golf course. A sandbagger can inflate his handicap index by selectively leaving out his best rounds of golf when he posts scores for handicap purposes.
Then, when the sandbagger enters a tournament, he claims, for example, a handicap index of 18 when, in fact, his true handicap might be closer to, as an example, 12. Voila, the sandbagger has just bought himself six extra strokes off his net score, and improved his odds of winning his flight or the tournament.
Sandbaggers are, at base, cheaters and hustlers. Golfers who are found out to be sandbaggers are often ostracized and always looked down upon.
Winning a tournament or bet in this fashion is called "sandbagging." A golfer who has won by sandbagging is said to have "sandbagged" his opponents.
Nuff said LOL