1.
flutter kick; up-and-down leg kicking
The alternating up-and-down kicking of the legs used in the front crawl and backstroke. バタ mimics the flapping sound; 足 means legs or feet.
Related Words
Compare:
平泳ぎ (breaststroke)
Compare:
ドルフィンキック (dolphin kick (swimming))
Related:
クロール (front crawl, freestyle)
Related:
ビート板 (kickboard (swimming))