A MC who is low on defensive skills will miss all his headers at set plays, he will also give away many fouls and pick up more yellow cards, if his physical and mental attribute are low also morale drops more than normal. IMO
I forced one of my MC's attacking skills so they were 4 skill points higher than the other two, the above was happening all the time, now I've almost brought them level, problem solved.
What use is a ST who cannot head a ball or is as slow as a donkey?.