Yates, 20, has joined the Hawks on a one-year dela after making 21 appearances for Saints’ senior academy in 2010.
Director of Rugby Darren Williams said: “Andy hits hard in defence and prefers the physical side of the game and loves to offload. He was awarded a squad number in 2010 but failed to force his way into Mick Potter’s plans. He was highly thought of by Daniel Anderson and was the Man Of The Match in St Helens Academy Grand Final victory against Wigan in 2008.
“Without a doubt he is a real coup signing for the Hawks as he was chased by Whitehaven, Oldham & Leigh and will be a force to be reckoned with as the club looks to consolidate in the Championship.
Williams added: “Andy has already shown his enthusiasm and desire in his first week at the club and he has good habits instilled into him during his formative years at the Saints.”