Here is one way.
Let $M$ be the maximum and $m$ be the minimum number of bounces among all the balls. Then the rating is just a matter of rescaling $m \le x \le M$ to $1 \le y \le 10$. The following function does this: $$ f(x) = 1+\left \lfloor 10 \frac{x-m}{M+1-m} \right \rfloor. $$ Then $f$ will map a ball's number of bounces, $x$, to an integer between 1 and 10, inclusive, with the property that if $x_1>x_2$, then $f(x_1) \ge f(x_2)$. More bounces results in a higher rating.
To get a lower rating with more bounces, just subtract $f(x)$ from 11: $$ g(x) = 10-\left \lfloor 10 \frac{x-m}{M+1-m} \right \rfloor. $$