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Soccer BEEF!!!!

D.C United coach Ben Olsen clearly wasn't too pleased about Alexi Lalas' comments on Wayne Rooney -- because now he's throwing some shade of his own.

Earlier this week, Lalas told us he wasn't too pumped about the MLS team working on a deal with Rooney -- because the guy's essentially a has-been.

"For me, Wayne Rooney doesn't move the needle," Lalas said ... "It might fill some seats, but not that many seats."

Play video content 5/9/18 TMZSports.com

Olsen tells TMZ Sports ... the deal with Rooney isn't done yet -- but he's already going to bat for the striker ... with a shot at Lalas.