A barrage of ice shards quickly followed after the first one was demolished by Leon's hardened skin. The ice shards were all fast, thick, and very sharp, but that didn't stop Leon from demolishing most of them upon contact.
Using his speed to guide him Leon was able to keep up with the speed of the incoming ice shards. It wasn't that Leon had speed thinking or anything but something close to that.
When a person with the speed ability runs, their brain has to also function at that same speed in order to make sure the person stays on track and doesn't hit a random wall or trip and fall while running fast.
Leon is basically using that skill where his brain is processing things extremely fast but he is staying in one place and not actually moving his legs much. He is instead using that speed in his arms so that he can block every single incoming projectile and smash it into a million pieces upon impact.