If this behavior appeared all of a sudden, and your son has otherwise been behaving normally, it indicates that something has changed in his environment and the change is upsetting to him. So, in addition to managing the behavior, it is crucial to figure out what has him so unsettled.
Relative to managing the behavior, he should be placed in time out immediately when any dangerous behavior occurs. He should be expected to sit quietly in a chair fora period of ten minutes or so. When the time out ends, he should be asked about the behavior that resulted in the time out. After the time out, he should play alone for fifteen minutes or so, and then be allowed to pay with one other child (in other words, he shouldn't proceed from time out to playing with a large group of children right away).