Just be careful what observations you link to changes. Spitting can affect anyone, its an 'Achievement' outwith your control so there has to be a chance of getting it. MCs tend to get more cards imo so its always possible without a change of role - but that doesn't mean cards and armband is not.

It really depends on how a Captain's performance affects the team - we don't know but its best to assume it does (just in case). If the cards are giving him poorer ratings then I'd be inclined to pick another player (again just in case). But you seem to indicate its not so its your choice.

I tend to choose a good consistent performer - I switch between choosing one based on fitness and creativity too. But I don't give it that much thought as long as my Captain is getting decent ratings - tbh I really don't think about it unless team form is down and I need something to blame other than me. >.<