The basketball player in the blue uniform is guarding the player in the orange uniform, who has the ball.
A orange uniform basketball player with ball is guarded by, a blue uniform opponent team player
If one is guarding then their opponent is being guarded.
This is a rephrasing of the previous sentence from a different point of view regarding which player has the ball, and who is being guarded.
If the blue player is guarding the orange player with the ball, then the orange player with the ball is guarded by a blue player.