PHILADELPHIA — In a record year for gun violence at high school sporting events, Da’Vion Harper played a football game Wednesday with a somber tribute written on the shirt beneath his jersey: “R.I.P. Micah.” Beneath his helmet, Harper drew the number 10 on one cheek and a cross on the other.

Last Friday night, 10-year-old Micah Tennant attended a playoff game in southern New Jersey between Pleasantville High School and Camden High School. The game was interrupted in the third quarter by what the authorities are investigating as a retaliatory shooting. Three people were wounded, including Micah, a fifth grader who was apparently sitting behind the intended victim.

The game resumed Wednesday in a cavernous, but almost empty, N.F.L. stadium, closed to the public except for several hundred family and friends of the players. Hours before, Micah had died from a gunshot wound to the neck. What was intended to be an afternoon of renewal, resilience and defiance became another tragedy in what is a rare but increasingly worrisome occurrence — gunfire at high school sporting events, which are supposed to be among the most celebratory and safest places.