[pygy_]

In this case, the temporal sequence suggests a causation.

A non-causal association would have to be induced by a confounding factor that first causes teens to play violent video games then to behave aggressively, but never in the other order.

The causal effect is reinforced by the dose effect in the context of this temporal sequence, i.e. the more hours they play per day, the more likely they are to behave aggressively.

[gojomo]

A non-causal association would have to be induced by a confounding factor that first causes teens to play violent video games then to behave aggressively, but never in the other order.

Yes, but not "never in the other order": just more often/strongly in the games-first order.

And I don't find such confounding factors hard to think up for 9th-12th graders: difficult family life; social problems with peers; substance abuse; academic performance pressures; etc.

If a teen were to react to any of these, first, by escaping into violent video games (as a relatively easy temporary mood boost), but then second, with measurable aggression, it would fit the sequential relation seen. But we wouldn't know with any sort of confidence if the violent-gameplaying interim behavior worsened or lessened the eventual aggression.