On April 11, pitcher Jeremy Affeldt addressed the spectators before a baseball game between the San Francisco Giants and the Los Angeles Dodgers.

"We play with a lot of competitiveness on the field," he said, his voice breaking. "But when the last out is made, that rivalry ends on the field."

Affeldt's plea for peace came 11 days after Bryan Stow, a Giants fan from Santa Cruz, was savagely beaten in the parking lot outside Dodger Stadium. Stow suffered major head injuries, and he's still hospitalized almost five months later.

We have yet to learn their names, but three more young men who attended a ball game left in ambulances — two of them shot, the other beaten unconscious at Candlestick Park on Saturday.

That's quite a score sheet for a meaningless preseason football game between the Raiders and the 49ers. But even if the cross-bay rivals were squaring off in the Super Bowl, there's no justification for thuggery in the stands or the parking lot.

Police have yet to make any arrests, and it's not known if the worst violence resulted from conflicts between fans of the opposing teams. But does it really matter?

Predictably, both teams promised to review stadium security. And, also predictably, they emphasized that just a small fraction of the fans were responsible for the violence, which also included at least a dozen fist fights in the stands.

True enough. Most fans turn out to see top athletes compete, not to pick fights. Those fans, directly or indirectly, also provide the billions of dollars that make pro sports a fabulously lucrative business for the players and owners. That should be ample motivation to maintain a family friendly atmosphere.

Do fans have reason to fear for their safety and that of their families when they fork over $100 or more for tickets to a ball game?

Regrettably, we can't answer that question with an unequivocal no.

Anyone who regularly attends pro sports events knows that public drunkenness. vulgar tirades and fisticuffs are becoming practically as common as home runs and acrobatic catches in the end zone.

If the promoters don't ensure that there is adequate security, fans will stay home. By and bye,they might turn off their TVs, too. For teams seeking public money for new stadiums — the 49ers among them, and possibly the Raiders, too — it's also crucial that voters don't see ball parks as battle zones that drain police resources.

After Saturday's debacle, 49ers owner Jed York said parking lot gates won't open as early on game days, tailgate parties will be prohibited after kick-off and inebriated fans will be turned away at the turnstiles. He also asked the NFL to stop scheduling preseason games with the Raiders.

But "degenerate behavior," to borrow York's description, didn't begin last week, and it isn't limited to the preseason or games against the Raiders. The 49ers acknowledged as much when they started revoking season tickets last year from fans identified as troublemakers.

Fans can help by pointing out thugs and drunks, but the teams and leagues must provide a safe environment. That means hiring adequate security and controlling alcohol consumption — in the stadium as well as in the parking lot.