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NBA player Denzel Valentine got embarrassed at the Drew League in L.A. recently ... and now the man responsible for dropping 44 on DV is telling us why it had to be done in such savage fashion.

The man's name is Frank "Nitty" Sessions ... the reigning Drew Leauge MVP and triggerman for The Game's team, "Birdie's Revenge."

Sessions' beatdown of Valentine instantly went viral ... and when he spoke with TMZ Sports, he told us in this case it was a little more than a day's work ... it was PUNISHMENT.

"He said something that bothered me, that most NBA guys I play with would never say to me."

We asked Nitty what Valentine said to him ... and, while he wouldn't say exactly, he gave us an idea when we asked if DV referenced the difference in the two men's bank accounts.

"Oh, of course he did. That's why I lost it. It's two lines and we both playing for free right now. In between these lines that don't got nothing to do with it."

BTW -- Sessions ain't broke. He's been getting money playing ball overseas for years, and basketball pays all the bills for him.