Thanks. We had an issue with a trade that was processed today (accepted yesterday)... leaving me without a SS eligible for this week.. i.e. my SS didn't play on 4/16.. the one I traded for did. So.. I had 0 SS eligible players on my roster for "this week" and had to add someone that didn't play yesterday so I had someone eligible at that position.. I guess if I didn't add someone (which i did just to be safe), my roster for this week would've been declared illegal.
You just won't get points for that slot that week. You don't forfeit the entire match and it is not deemed illegal that way as long as you have the min/max for that position filled on your whole roster.