Concussions and ADHD are a mixed bag. Most experts say ADHD meds are counter to good concussion recovery.

A very small number has found ADHD meds to be beneficial to a recovering brain.

Concussions can reduce the brain's ability to ignore sensory stimuli/distractions. This can made ADHD worse.

The risks in soccer for concussion are:
1. Heading the ball
2. Getting hit in the head by a hard kicked ball.
3. Hitting head to head against an opponent. More common than you would expect.
4. Getting kicked in the head by a high kick.

Some leagues outlaw high kicks and heading the ball.... ???

If he has extra risk from a brain bleed because he has a bleeding disorder, I would be extra cautious about soccer.

Years ago, this forum had large numbers of members who were having serious struggles after getting concussions playing soccer.