Well, I played and later coached for several years. I couldn't tell the speed which the defender approached and how much he bumped the offense player. But I believe Dziadzi is correct and a direct kick is appropriate. Theses days, the next offense could be a warning, maybe two.... then a yellow. But a good referee just tells the defender, after the ball clears, to knock it off and watch the hands in close or more than a direct kick will result.