Four-dot fire radical at the bottom, the indexing radical and underfoot form of 火. The flames anchor the harsh, fierce, deadly imagery of 煞 - an evil spirit, a malign force, a violent stop. Same fire-bottom in 热 hot, 烈 fierce, 焦 burnt, 熟 cooked.
Upper left 刍 supplies the sound - chú drifting to shà/shā through an old-reading alternation. 刍 itself pictures a hand grasping a bundle of cut grass for animal fodder. Same phonetic also drives 雏 chick (young bird) and 趋 to hurry, both keeping the chu reading.
Upper right 攵 is the strike radical, the side form of 攴 picturing a hand holding a stick. It contributes the meaning of forceful action - bringing something to a halt by striking. Same component in 收 to gather, 改 to alter, 故 cause, 政 government.
