What is a hat trick in soccer?
Three goals by one player in a single match. It's rare, it's enormous, and tradition says the player gets to keep the match ball.
Explain further
The one-liner tells you what it is, so here is why it matters and where the name comes from. In a sport where a typical game might finish 2-1, scoring three times alone is a huge feat. A single player has to out-do entire teams, which is why hat tricks make highlight reels and why fans chant a scorer's name when the third goal goes in. There is no rule that rewards a hat trick with extra points on the scoreboard; it is purely a personal milestone, like a baseball player hitting for the cycle.
The keepsake tradition is the famous part. After the game, the match ball is often signed by teammates and handed to the scorer. The term itself comes from cricket: in the 1800s, a bowler who took three wickets on three consecutive deliveries was rewarded with a hat, and the phrase later migrated into soccer.
One thing that trips up newcomers: the three goals do not have to be consecutive, and it does not matter how they are scored, whether with the left foot, the right foot, or the head. A "perfect hat trick," one goal with each foot plus a header, is a fun bonus, but any three goals by one player in a single match counts.