4 seam grip

My son has started working on throwing a 4 seamer with his middle and index fingers touching or very close to touching. He seems to have picked up some velocity with this grip. Why is this? He does not have as much command with this grip but still throws for strikes.

This is because sometimes when kids spread apart their fingers too wide, it becomes almost like a splitter since it will kind of roll off inbetween their fingers. When their fingers are close together, it allows them to put more overall force behind the ball. Now it probably gained your son some velocity, and the reason for the command issue is more because he isn’t used to the grip and sometimes it probably just slips out of his grip.