The issue with the football players returning to play is more directly a result of second impact syndrome. The sooner they returned to play, the weaker their brain is at handling a second impact. Some ponder whether there is also a component of depressed motor skills (clumsiness or slowed reactions) from the concussion that predisposes the injured player to the risk of a second concussion.

As for snowboarding, the impacts the brain feels from riding the hill and butt plants that are common to snow boarding could have the same effect as a second concussion. The vibrations of a corduroy snow surface left by the groomers can also manifest as a concussion.

Vibrations can be more easily transmitted to the brain because the vibration wave pattern cannot be absorbed as readily by the spine.

I suffered a concussion from driving down from the ski area on a rutted road. It can be similar to the shaking of a wooden roller coaster.