Gladiatorbeast vs Battle Fader

Ok this happen to my Friend a while back at a regional. A guy playing Glads attacks with a glad beast attacks and destroys tree-born frog, so then then he try to attack direct with his second glad, my friend drops battle phader. The big Question is can the glad play tag with the monster that attacked the monster. The reason it is questionable is because Glads tag at the end of the battle phase, and battle fader says it negates the attack and end the battle phase. My friend said he couldn't tag and a judge ruled for the glad player. So who was right my friend or the judge?

Yes, Gladiators that went through dmg step will be able to tag.

Gladiator Beast effects take place during the End Step of the Battle Phase. Battle Fader skips every subphase of the Battle Phase and takes the game directly to the End Step of the BP, wich is where tagging effects activate and resolve.

Ok, i thought it would not because battle fader would send the turn straight to main phase 2 so the end of the battlephase wouldn't happen.

That's a common mistake.

"When you end the Battle Phase with "Battle Fader" the game moves to the End Step of the Battle Phase."

http://yugioh.wikia.com/wiki/Card_Rulings:Battle_Fader