If you have the ball, and someone on your team purposefully gets between you and an opposing player who is trying to tackle you, then your teammate is guilty of obstruction, which is a penalty.

When a player and an opponent are running for the ball, either player must not charge or push the other except shoulder-to-shoulder. For doing this the referee would award a Penalty kick to the opposing team. A player must not intentionally move or stand in front of a team-mate carrying the ball thereby preventing opponents from tackling the current ball carrier or the opportunity to tackle potential ball carriers when they gain possession.

A player must not intentionally move or stand in a position that prevents an opponent from tackling a ball carrier. A player must not intentionally move or stand in a position that prevents an opponent from playing the ball.

 

When any sort of obstruction occurs the regeree will award a penalty kick to the team that was blocked.