You will get/be hit by a ball - is there a difference?
Solution 1:
In this context, the word get means
to become or cause to become or act as specified: to get a window open, get one's hair cut, get wet
This becoming sense is closely related to the simple future tense of to be in your examples.
. . . he will get hit by the ball.
. . . he will be hit by the ball
This even works in the past tense
. . . he got hit with the ball.
. . . he was hit with the ball.
This usage of get is often followed by reflexive pronouns such as himself, yourself, myself.
I don't want to get myself in trouble
While your two sentences can be viewed as equivalent, some might read a slight suggestion that get hit implies some personal involvement or causation.
He got in a fight.
seems to subtly suggest more culpability than
He was in a fight.