They're too fast to catch up with (i.e., from behind). But if someone sprints straight into your fist, that person will be hurt even if your fist itself is full

They're too fast to catch up with (i.e., from behind). But if someone sprints straight into your fist, that person will be hurt even if your fist itself is fully stationary. In fact this probably makes them somewhat more vulnerable to an interceptor's warhead's shrapnel: even lesser damage, survivable for a slower target, might be much more serious for a target flying at high Mach speeds (not the mention the imminent "Columbia syndrome" of very hot air suddenly inside your vehicle).