The answers to the following clues will have something in common.

1. Appear, often unexpectedly
2. Butt heads, as in disagreeing
3. Assume the fetal position
4. Go berserk
5. Halloween activity involving water
6. Retrieve baseballs at batting practice
7. Scientific explanation of the birth of the universe
8. Search thoroughly
9. Dismiss rudely
10. Be patriotic, sometimes to a fault

Answers:

1. Crop up
2. Lock horns with
3. Curl up in a ball
4. Flip out
5. Bob for apples
6. Shag flies
7. Big Bang Theory
8. Comb
9. Brush off
10. Wave the flag

Credit: Chicago Tribune Crossword
Robert H. Wolfe (#1-7 - adapted)
THE GANG'S ALL HAIR