Seems like u don’t fully understand how warriors work.
They need to either hit with their auto attack or get hit to generate rage (their resource). The “getting hit” part is the biggest rage generation part, especially if u’re not dualwielding with fury spec.
This means, that when u place ur shield on him, he is unable to generate rage, because he’s no longer taking damage. And without any rage he can’t use his AoE abilities to actually keep the aggro on the mobs, meaning they’re very likely to run around and wipe the group.
Now, i wasn’t there, but i feel he should have taken smaller pulls, and maybe ur group composition wasn’t the greatest for spellcleave / meleecleave.
Also, 1 last thing. naming and shaming is against the ToS and might get u in trouble on the forum. Can be read on this link:
Welcome, Please Read! - #3 by Aerythlea-2611