dominant foot
Refers to the foot a person naturally prefers for kicking, stepping, or leading. Often contrasted with 軸足 (pivot foot).
彼は利き足で強くボールを蹴った。
He kicked the ball hard with his dominant foot.
利き足が
Which foot you step forward with changes depending on whether your dominant foot is right or left.
Compound of 利き (kiki, 'effectiveness, dominance') + 足 (ashi, 'foot'). The exact historical derivation is uncertain, but the word follows the pattern of 利き手 (dominant hand).