Seeing what happened reminded me of something that I learned about in EMT class that was probably the cause of the issue:
From Wiki:
Commotio cordis (
Latin, "agitation of the heart") is an often lethal disruption of
heart rhythm that occurs as a result of a blow to the area directly over the heart (the
precordial region) at a critical time during the cycle of a heart beat that leads to the commotio cordis by disrupting the normal heart electrical activity, followed instantly by
ventricular fibrillation and complete disorganization of the heart's pumping function.
[1] It is not an event caused by mechanical damage to the heart muscle or surrounding organs, and not the result of heart disease.
[1]
Currently the survival rate is 58%, which is an improvement since the years 1993–2012, when only 34% of victims survived. This increase is likely caused by prompt
cardiopulmonary resuscitation (CPR), access to
defibrillation and higher public awareness of this condition.
[1][2]
Commotio cordis occurs mostly in boys and young men (average age 15), usually during sports, most frequently baseball, often despite a chest protector.
[1] It is usually caused by a projectile, but can also be caused by the blow of an elbow or other body part. Being less developed, the thorax of an adolescent is likely more prone to this injury given the circumstances.
[1]