Singer countersues DJ, claims he grabbed her a**

Taylor Swiftwon't let go if she's been disrespected!

According to Swift's recent legal documents, Swift says she's 100% sure David Mueller lifted her skirt and grabbed her butt in 2013 at a backstage photo op for her Denver concert.

READ MORE: Taylor Swift Singer named highest-earning music star of 2015, rakes $1m per day

As we previously reported, Mueller initially sued Swift claiming he was fired from his radio gig after the singer claimed the radio jock groped her.

Mueller now claims the assault was carried out by another guy ... but in her docs, Taylor insists Mueller was the one who got handsy, leaving the singer, "surprised, upset, offended, and alarmed."

READ MORE: Taylor Swift's the new queen of Instagram with 50m followers

Taylor's asking for damages to be assessed by a jury, and says she'll be donating any money she wins to women's charities.