Hello, my cat had a little crusty area on his head and when I pulled it the hair fell off. Could this be just a wound or must it be ringworm

It could be either one, without seeing it that would be difficult to determine. Ringworm usually has a rounded appearance with scaly edges, but in a cat it will often take on different looks. Do an image search and you will see how varied they can be. If you have other cats or pets or he is an outdoor cat the chance that it is a wound is good. Check in the area that you found the first spot and feel for other scabs or bald or crusty places. Generally a bite wound will have more than one puncture since the long canine teeth in the front are what causes the damage.

And, when a bite wound gets to the point that the hair is 'slipping', there should be a pus pocket developed beneath the hair loss area that you can feel. Gently push... it won't hurt the cat.

Ringworm is contagious and fairly common with cats, especially if their immune system is not quite up to par. Best check this out with the vet since you can catch ringworm, too. (If it is that)

If the cat has an ear infection and scratches other places after its ears the bacteria can be transferred from the claws to any were on the body. Hair loss, pus, and wetness and be symptoms.