which player weares the biggest helmet?
Without more specifics as to what you're asking about (regarding individual head size? head coverage per sport?), I'd have to say: The one with the biggest head!
The Society for Creative Anachronism offers full-force fighting (with rataan swords) and they take an immense beating. Their stringent safety rules state that the helm must meet the shoulder armor, and take a killing blow.
Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them