Baker Mayfield: Haters Can Hate, I'm Gonna Train

Baker Mayfield knows not everyone is thrilled the Cleveland Browns took him with the #1 overall pick in the NFL Draft -- including Jim Brown -- but he's ready to bust his ass to win 'em all over.

The former Oklahoma Sooners quarterback touched down at LAX -- cowboy hat in tow -- and told TMZ Sports he's not messing around, it's all business from here.

No partying, no giant spending spree ... the 23-year-old Heisman Trophy winner says he's laser focused on training for the 2018 NFL season.

As for Jim Brown and other critics who wanted Cleveland to take Saquon Barkley or any of the other top QBs instead ... Mayfield doesn't seem too bothered -- telling us, "Everybody has their opinions. They're entitled to it."