Trinity Rodman -- who went #2 overall in the National Women Soccer League draft in January -- explained on social media on Monday that the former NBA star popped up out of nowhere at her Washington Spirits game on Sunday.

In her post, she said it's the first time she's seen him in a very long time ... and called the reunion at the game against the North Carolina Courage "an extremely emotional one."

"Yes Dennis Rodman showed up to an Nwsl game, but also my dad, after YEARS surprised me at a big game in my career," the 19-year-old said. "I was shocked, overwhelmed, happy, sad, everything."

Trinity -- who shared a photo of the two at the game in her post -- says Rodman hasn't been in her life much ... and explained sometimes they go months without seeing each other.

"My dad doesn’t play a big role in my life at all and most people don’t know that, we don’t see eye to eye on many things," Trinity said.

"Being in spotlights has been hard for us, him and me. We don’t have the best relationship, but at the end of the day he’s human I’m human."

But, Trinity did say she hopes their emotional moment on the pitch will be the start of a better daddy-daughter relationship.

"He's my dad, and I’m his little girl that will never change," Trinity wrote. "I will improve and look forward everyday as I hope he does."

Dennis had Trinity and his son, Dennis Jr., with Michelle Moyer, who he met in 1999. They married in 2003, but Michelle filed for divorce in 2004. It was finalized in 2012.