A One Punch Man wikia states there is a battle between Tank Top Master and One of Bofoi's drone. Which chapter/version of One Punch Man (webcomic/manga/audiobooks) is this battle in?
I think you are talking about the Vol 7 Bonus Manga 1: Big Construction.
As for their battle:
The association thought they were under attack because of Bofoi's Drone, at that time Tank top master and other tank top heroes is at the hero association so they are deployed to "defend" their base.