For this you need to max out the Hit Power upgrade which has 4 levels which requires a total of 2500 XP
1st Level - 275 XP
2nd Level - 500 XP
3rd Level - 700 XP
4th Level - 1025 XP
You earn XP from completing levels, 300 XP from regular levels and 450 XP from boss levels with no XP modifiers and no ball losses in a level.