Winter isn't expecting to run right into Steve, either, so though he flails a little, between Steve over-balancing and grabbing him, and the uneven balance of his metal arm, he goes over, too.

Thankfully, or perhaps unfortunately, he's also grabbing for Steve with his non-flailing hand, so he lands in a heap on top of Steve.

He stays there for a moment, panting a little, before he says, "Ow?"