E.L.
It sounds like he used to be on the nebulizer, and is now using an inhaler. Is he using a spacer with the inhaler (a wide tube that goes between the inhaler and his mouth)? If not, ask his doctor for one -- they make it much easier for kids to use an inhaler.
In general, if he's having an attack when he plays sports or runs around, it sounds like his asthma is not well controlled. He should have two different types of medicine -- a long term controller, like Flovent or Qvar, and a short-term rescue medicine, like Albuterol or Xopenex. The controllers won't do anything when he's already in an attack, and the rescue medicines won't prevent an attack.
If this doesn't sound familiar, insist that someone at your doctor's office talk you through it, or send you and your son to a class. It's important.