This is a story-related achievement and cannot be missed. It will unlock upon defeating Zed, the Stage 1 boss of the game. Like every boss, Zed has 3 phases.
- Phase 1 - Dodge his screaming letter attacks with button and hit him from behind. Repeat.
- Phase 2 - Destroy all the speakers Zed is standing on with your chainsaw then he will leap to a huge speaker that you must destroy via a QTE. You'll also have several quick time events to dodge his attacks. As soon as you dodge get right back to destroying the speaker.
- Phase 3 - This is where you will get the Watch Out For The Balls achievement. Refer to that section for instructions on defeating Zed.
Upon defeating Zed this will unlock.