Good points my allmymarbles. You might want to observe him at preschool and see how they work with him.
We do see situations like this when there is a new younger child involved. Do you have any other kids? and if so - how old are they?
Also, you said, "he is under dr at the hospital". Are you saying he is under doctors care at the hospital? If so - for what?
Nowadays whenever a child misbehaves ADD/ADHD is usually on the list of suspects. Bad behavior can be caused by diet, by environment, by permissive parenting, and, possibly, by an emotional problem.
Your son is well-behaved in school which suggests that he is not a candidate for an ADD diagnosis. As for his being a little wild and fearless, that is not unusual in a four-year-old. You might want to discuss your problem with a behavioral specialist.