His eyes went from the engineer to the other super soldier when Stark directed his attention that way, and he didn't suppose it was too much to ask. He'd hit Steve much harder before without causing any permanent damage that he was aware of, and given it would be with his weaker hand, he didn't think it would cause any problems overall. Steve was the one to suggest it...

The soldier stepped in front of Steve and only waited for a split second to allow him to brace himself before he silently threw a punch at his face. It was definitely enough to knock a lesser man off his feet, and enough to topple Steve over if he wasn't properly prepared for it.