The United States women’s water polo team has dominated in the Rio Olympics. We asked Natalie Benson, a two-time Olympian, to tell us how players get an advantage.

Women or men, it’s well known that players will do anything they can get away with in water polo. Referees stand poolside and are only able to make calls based on what they see from above.

Benson explained that “because players can’t touch the bottom of the pool, they must find ways to create their own leverage by using their opponents.” Players are constantly jockeying for position and playing what Benson referred to as “the game within the game” by wrestling for an advantage over their opponent below the waterline. What looks like a clean pass here is actually the result of a swift kick to the gut.

Here, a defender grabs an ankle to keep her opponent from swimming away with the ball. This move is illegal and would normally be called as an exclusion foul, but it happens often underwater.

Referees check for long finger and toe nails before each match, but players can still get scratches. Benson explained that players will grab onto swimsuits and “hold them like handlebars for controlling their opponent’s position, like in judo.” While most of the time there is no intent, this sometimes results in suit-lines getting scratched up.

Players aren’t supposed to dunk or swim over their opponents, but such fouls occur regularly, to varying degrees. If a referee doesn’t see the start of the play, it’s often difficult to know whether what they are seeing is a foul or if a player is just faking, so no call is made.

The offensive center position, similar to a basketball center, endures the most punishment. In the case above, the center’s defender is holding her opponent with one hand and jabbing her kidneys with the other. Benson said that if this happens fast enough, with the ball in play elsewhere, the referees’ attention is frequently diverted and no call is made. Provocative aggression is often self-moderated, however, because this sort of brutality begs for retaliation.