During an FBS game some years ago, I observed two receiving team players hold hands during a kickoff return, and actually block an opponent. The BC was probably 15 yards away, and was tackled just a moment later, so the block had no impact on the result of the down. I passed on making the call, but, at the first TV break, I went to the special teams coach for that team and told him that wasn’t allowed, and warned them to not do that any more. I wrote that up on my foul report, and my Coordinator commented that this was the best way to handle that situation. This looks very similar. A “talk to” with the special teams coach to let them know that such action is not legal, and don’t do it again would be appropriate.
Had the BC gained additional yardage directly due to the block, I would have flagged it, without warning.