UFC super-fan Travis Barker says he's got Conor McGregor's back when it comes to his violent bus attack at Barclays Center ... even though he went a little overboard.
Don't get it twisted -- Travis thinks it's terrible other UFC fighters got caught up in McGregor's window-smashin' madness ... but the blink-182 drummer says Conor HAD TO retaliate after his boy, Artem Lobov, got strong-armed by Khabib's team.
"I would've probably done the same thing if someone punked my friend," Barker told TMZ Sports in Calabasas. "I love him to death ... crazy motherf**ker."
At the same time -- "I can't agree with everything he did ... he has to apologize."
FYI, McGregor bailed outta jail Friday and is facing charges of assault and felony criminal mischief ... but Travis says the UFC should "slap him on his wrist" and let him off so he can fight later this year.
We'll see ...