Football / Soccer / Calcio / Futebol / Fußball

You can be knowledgeable in more than one field

You can, but you need to prove it by showing your know knowledge in said field. In that case, you listen to someone talking about hockey that happens to be a successful footballer, not because he's a successful footballer

I don't know Cech outside of football, but I'm assuming the reason you and others (in particular, hockey people and drummers) listen to him on those topics and found it to make sense. Yes, without him being a successful footballer you'd never heard about him, but he still needed to prove himself on that

Then you also have the obvious that having certain issues in some issues raises your commercial value to a degree that hockey and drumming don't