What Causes Foaming At The Mouth And Shakiness On Being Punched Hard On The Face In An Exercise Induced Asthmatic Patient?

MY SON WAS RECENTLY DIAGNOSED WITH EXERCISE INDUCED ASTHMA AND RECENTLY WAS SITTING DOWN WITH NO EXERTION WHEN ANOTHER KID CAME UT OF NOWHERE AND PUNCHED HIM IN THE FACE WHEN I WAS CALLED A FEW MIN LATER HE WAS GSPING FOR AIR I CALMED HIM DOWN AND GAVE THE VENTOLIN PUMP. THEN AN AMBUALNCE CAME AND CKED HIS PULSE OX WHICH BOUT 20 MIN LATER WAS NORMAL. I WAS LATER TOLD BY A WITNESS THAT WHEN HE OT HIT HE WAS FOAMING AT THE MOUTH LIKE CLEAR BUBBLES AND SEEM TO BE SHAKING A LITTLE CAN YOU PLEASE SHED SOME LIGHT ON WHAT MAY HAVE HAPPENED. THE INCIDENT WAS WEEKS AGO AND HE HAS BEEN FINE SINCE THEN