taking methotrexate every other week

Mild traumatic brain injuries, or concussions, are rare but can happen when the velocity of the tennis ball is higher than 40 meters per second. To put that in perspective, that’s faster than a cheetah can run.
A ball striking the side of the head was most likely to cause a head injury, compared to being struck in the forehead or the top of the head.
Head injuries were also more common when the ball hit someone at a 90-degree angle versus a 30- or 60-degree angle.
But spinning of the ball was not found to have any significant impact on causing a head injury.

How the study was done