Flavor Flav Hyping Olympic Water Polo Unexpected Says Capt Maggie Steffens

Flavor Flav's revving up the hype train for the U.S. women's water polo team, and one of its star players, Maggie Steffens, is still floored by how they landed the celeb endorsement.

Maggie, the team captain, and Flav joined us for a chat Monday on "TMZ Live" ... and she admitted she definitely didn't expect the rapper to answer her IG call for more support for her team.

Fact is, the team's won gold at the last 3 Olympic games -- but still needed something, or someone, to juice TV ratings this summer in Paris.

Enter Flav, who came through by responding to Maggie's post ... "As a girl dad and supporter of all women's sports – imma personally sponsor you, my girl, whatever you need." He topped it off with, "That's a FLAVOR FLAV promise."

Flav is actually finalizing a deal to make him the team's official sponsor, and he tells us he's passionate about the whole thing ... 'cause despite the team's already impressive Olympic record, he feels like they're not getting the recognition they deserve.

His motives are as simple as they come: he just wants to give back and help the girls reach their goals -- and for that, Maggie couldn't be more grateful, especially since Flav's been bringing loads of positive energy to their unexpected partnership.