And indeed Marcus did come at him, lunging forward with his fist cocked back and prepared to slam into John's jaw.  
"Marcus stand down!" Barked Kyle from behind, having sat back thinking Marcus would let John go after knocking him down.  Now seeing his soldier charge the other unprovoked he looked to intervene. Marcus didn't slow, but involuntarily instinctual obedience to his superior made him flinch when yelled at and he faltered.  The result being his aom was thrown off and instead he slammed into John's shoulder.