Very common. Two reasons: 1. Complete a CT scan/other testing to check for acute injuries as quick as possible like aortic transection, cardiac tamponade, pneumothorax, head/neck injuries, etc. without having to deal with him moving with a breathing tube in and 2. If suspected injury to the brain after the event, medically induced coma is necessary for targeted temperature management, which is cooling the body after a cardiac arrest for a period of time to try to reduce injury to the brain after the event essentially.
But this is speculation in general of the event. I want to make that clear that I can’t be certain what happened but it looks like commotio cordis. Just a bit odd the timeline of him standing after the hit then passing back out and then losing pulse again. But the heart does funky things when just starting to code and it’s conceivable that the built up blood pressure from the beats of the heart prior to the traumatic arrhythmia allowed him to stand.
Source: pure speculation of the event and report reading, but I’m an ER physician.