go at it

verb4

1. •
   As go at + it; spoken emphasis typically on 'go'.

   • I can't figure out this problem. I've been going at it [going at the problem] for hours now.
2. •
   (informal) To engage in some activity, especially vigorously or enthusiastically.

   • We were all going at it like crazy, trying to get the job finished before the deadline.
3. •
   (slang) To fight or argue.

   • Joe accidentally spilled his drink on Eric, Eric got up and insulted his mother, and before you know it, they were going at it.
4. •
   (slang, euphemistic) To have sex.

   • I walked into my dorm room and caught my roommate and his girlfriend going at it.