strike, hit, beat, attack, fight
擊 centers on forceful physical contact: striking, hitting, or beating, and by extension attacking or fighting.
擊 combines 手 (hand) with 毄, which likely contributes the sound and the idea of striking. The modern Japanese simplified form is 撃.
The bottom 手 is a hand, and the upper part resembles a weapon or striking tool. Picture a hand gripping a mallet and bringing it down to strike.
For ゲキ, imagine a dramatic strike in a gekiga (劇画) style comic panel: the sound effect 'GEKI!' appears as the fist hits.