This is funny and all good until he gets tackled / pulled by the chain, the chain hurts / cuts his neck and then everybody will be "why did they let him play wearing jewelry?" I don't know what is hanging from that chain, if he has an edged object (i.e. cross) it could cause some damage to his neck if happens to be in the wrong angle at the wrong time, tucked or not.
Of course, we hoping none of that happens to him or anyone, but every time he runs a play with that thing on his neck there is a risk.