Em đọc trên wiki thì thấy Free Style đúng nghĩa bơi kiểu gì cũng được đấy cụ (tất nhiên là vẫn phải tuân thủ các rule)
en.wikipedia.org
Freestyle means that in an event so designated the swimmer may swim any style, except that in individual medley or medley relay events, freestyle means any style other than backstroke, breaststroke, or butterfly
Some part of the swimmer must touch the wall upon completion of each length and at the finish
Some part of the swimmer must break the surface of the water throughout the race, except it shall be permissible for the swimmer to be completely submerged during the turn and for a distance of not more than 15 meters after the start and each turn. By that point the head must have broken the surface.[5]