JACKSONVILLE, Fla. — The off-season had just ended. The competitors, the finest players of a football video game, had gathered on the riverfront in Jacksonville for two days of animated battle. The weekend’s tournament was their first sanctioned chance to show which game-winning moves of the “Madden” franchise they had unlocked.

Pride and cash prizes were their goals.

Then came the gunfire. Two players were killed. Another 11 people were injured, 10 by bullets. And the gunman, a 24-year-old player from Baltimore, was dead.

The fatal rampage on Sunday was yet another mass shooting in a state already familiar with the grim customs that come with bursts of gunfire. But the attack has also cast a light on the rites and rigors of competitive e-sports, a close-knit, screen-named world of streaming and sponsorships, supersized rewards and swollen egos.

“The suspect clearly targeted other gamers,” Sheriff Mike Williams of Jacksonville said of the gunman, identified as David B. Katz. He had been defeated in the tournament earlier in the day, then later pulled out a handgun. “The suspect walked past patrons who were in other parts of the business and focused his attention on the gamers,” the sheriff said.