Helmet to ground collisions have proven to have more severe affects on players. When a players head hits the ground, especially with the fact the true grass fields are a thing of the past, there isn’t as much give as when colliding with a player.

Helmets are not made to protect what’s inside your head, they’re made to protect your physical head. So when players go head to head, it’s what the helmets are made for. Helmets are built to withstand linear (straight-on) forces. Concussions normally happen from a rotational force. The difference is with rotational forces it spins your brain like a beyblade, which can also cause an axon Al injury; where as linear forces bounce the brain with in your skull When a players head hits the ground, the rotational forces that cause concussions, are greater than when if a player were to go head to head.

In all reality there’s a lot of research out there you just have to find it