Achievement:Ball Eater
From GMod Wiki
Ball Eater Eat 200 balls Difficulty:
How to:
If you go to the menu with Sents and spawn a Bouncy Ball you can use it (eat it) and it will give you a small amount of health. You can hold the use key and simply run into them as it's not required to repress the button, so simply spawn a bunch and run around while holding use.