How should i limit my son's activity after a ruptured spleen?

Be cautious: Follow the hospital discharge instructions which should include avoiding strenuous activities, and definitely no contact sports. If you did not receive any discharge instructions, contact you discharging physician for further instructions.

Depends: Depends what was done. If he had a surgery that removed his spleen, then incisional pain will be a safe guide for his activity. If however his spleen is left in place, then depending on the degree of laceration, time off from contact sports is dictated. Speak with the doctor that cared for him in the hospital.