both systems were used - sometimes on a single shield - for example a hoplon (Greek infantry shield) has a tube the forearm passes through, but it's also held at he rim by the hand.

Similarly many much later shields such as Norman kite shields are secured by straps at the forarm and also held by hand.

"Centre grip" shield such as roman & Gallic Scuta and Viking roundshields are well known but seem to be predominatnly used by swordsmen

easy enough to deliver a solid bow with a spear held one-handed - it's just that the blow can be relatively easily deflected.