No, an average is not calculated by only the first ball. But, how a bowler rolls the first ball deterines what type of bowler they are, right, left or 2-handed.
Let me be clear. This IS a new Youth League Rule. A Youth bowler has to maintain a book average by whether they use only right, only left or whether they use a 2-handed release. And, this is only the first ball, by definition.
The succeeding rule is for spares where a bowler has to use the dominant hand from the first delivery.
So, a 2-handed bowler, supporting the ball with their right hand cannot use a 1-handed delivery with the left hand for spares.
Sounds correct for the youth league. Still, it seems more discriminatory than anything. If the first ball determines whether the bowler is one-handed or two-handed, yet ADULTS are allowed to switch at will, the rule cannot apply to ADULTS. If the rules don't apply to adults, how is it fair to limit YOUTHS with such a rule? Shouldn't it be the choice of the individual, maybe along with the advice of their coach?
I wonder if golf would ever have a rule that if a golfer swings with one hand, said golfer would have to ALWAYS use only one hand. That is, a YOUTH golfer. Makes no sense.