The linked site says :
A careful reading of official Major League Baseball Rule 6.08(b) suggests that in this situation, the batter would be considered "hit by pitch", and would be eligible to advance to first base.
They don't give the kinetic energy, though. This follows directly from K = (gamma - 1)mc2. With beta=0.9 , this comes to 1.29 mc2, i.e. 29% greater than the rest energy.
I always recall this illustration:
Half a dime is about 1 gram and a baseball is about 150 grams, so we're talking about 200 gram equivalent in kinetic energy at 0.9c. If the Hiroshima bomb was about 10 kilotons, we've got a 2 megaton explosion.
"That's the wonderful thing about science, one gets such wholesale returns in speculation on such a trifling investment of fact." - Mark Twain