MLB's Marcus Stroman Rips Broadcaster Over Du-Rag Quip ... 'Racist Undertones'

Mets star Marcus Stroman is NOT happy that a quip was made about his du-rag during a TV broadcast Tuesday ... with the pitcher saying the comment had "racist undertones" to it.

The remark went down during the 4th inning of the Diamondbacks' broadcast of the Mets-DBacks game ... when color commentator (and former World Series-winning manager) Bob Brenly threw a jab over Stroman's visible head covering.

"Pretty sure that's the same du-rag that Tom Seaver used to wear when he pitched for the Mets," Brenly said.

The comment was met by immediate backlash on social media ... with many finding it to be very offensive and racist.

And, when Stroman took to Twitter after the game ... he clearly agreed.

The…