I agree with CFsupporter that tops only get in the way, even so called sports bras tend to restrict your freedom of movement. With other kinds of bras and tops, the straps are always getting out of place or in the way, and many women tend to get distracted and try to cover up when their boobs pop out, whereas if you're not wearing a top you don't concern yourself with those distractions. Even in a so called "friendly" wrestling match, (is there truly such a thing as a "friendly" competition of any kind between two women?) the objective is to win and enjoy the match, the challenge, dealing with tops is frustrating and it detracts from the enjoyment of the contest.