So, when do you know when a head injury is a concussion? The truth is you don't really know until you've been checked out by a doctor. Any kind of head injury weather it being hit by a baseball bat, falling on the ice and hitting your head, tripping on the concrete and hitting your head, running into a wall, having someone open a door really quickly, falling off your bike with or without a helmet. You never know. You need to get it checked out. People have been hit in the head, gotten up, walked around, acted fine like nothing were wrong, seemed like they were fine and then it turned out to be something fatal. It's much better to be safe than sorry. Don't think that you can muscle through it. Always get checked out if you have a head injury. If you find someone whose unconscious, if you see evidence that they were hit in the head, their head is bleeding, they have a bruise on their head, no matter what, if they're unconscious call 911. But, also tell them that this is what you see. Always call for help. If you find someone unconscious and they're not responding to you, call for help. It is better to be safe than sorry. You never know when a little bump on the head can turn into something fatal.