'TMZ Hollywood Sports' -- Pro Surfer Beefs with Chanel ... Over New Gisele Ad

Gisele has surfed her way into the crosshairs of a pro boarder ... who says Chanel made a HUGE mistake by casting Mrs. Tom Brady in a new surf-centric ad campaign -- instead of someone more "authentic."

We spoke with Anastasia Ashley ... who says, "There are so many good looking surfers who also model. Why not choose one of them? It would've been a better ad."

And despite the fact Gisele does surf on occasion, Ashley believes the new ad is not going to go over well in the surf community -- "Surfer's are territorial. A lot will think she's a fraud."

Check out the segment -- Anastasia even has a message for Chanel honcho Karl Lagerfeld ... but it's not what you expect.

Make sure to check out the brand NEW episode of "TMZ Hollywood Sports" on Reelz -- every weekday at 8pm ET, 5pm PT.