[ProAgonist]

There's no evidence that getting a concussion means that in the future, you will get another concussion from less acceleration of the head as a result of sudden forces applied to the skull.

The source reads:

"We used to think that if you took a bunch of little hits, then you were more likely to get a concussion from a smaller impact," Broglio says. "But our findings don't support that."

Source: http://www.ns.umich.edu/new/multimed...young-athletes

[Mark in Idaho]

There have been various studies about second/subsequent hits and such with varied results. It is very difficult to adequately categorize those second hits or the force of the multiple little hits.

People still need to try to avoid hitting their heads.