Left stone radical - the indexing semantic. Smashing involves a heavy rock-like force dropped or swung onto a target. The radical correctly tags 砸 in the stone-impact family alongside 破 (break), 砍 (chop), 碎 (shatter), 碰 (collide). The colloquial 'to fail/bomb' sense extends from 'the result smashed flat'.
Right component supplies the sound (zā → zá, tone shift only). 匝 by itself means 'one full circuit, to encircle'. The encircling imagery dovetails neatly with the swinging arc of a hammer - phonetic with a faint mnemonic echo of rotational impact.
