What episode does Toby flenderson hit someone in the office?

Toby never hits anyone in 'The Office'

Perhaps you may mean 'hits on' as in flirts, and that occurred in 'Night Out' is Season 4 where Toby touches Pam on the leg while they wait in the building lobby to be let out of the parking lot.

Also, Michael tries to get Toby fired by provoking him to punch him, along with Ryan and Kelly trying to persuade as well, but Toby refuses. This occurred in 'Frame Toby' in season 5.