Fans belong in the stands, not on the field.
Still, in baseball there is sometimes a thin line between what is and isn't acceptable, especially when balls in play fly toward the outfield fences or into foul territory.
Or, say, when a major league team decides to rig up explosives and detonate them in center field.
Wait -- what?
Here are just a few of our favorite moments when fans became more a part of the story than they probably should have been.
(Please share your own favorites in the comments section. We know there are tons more.)
Oh, baby! (June 23, 2015)
When Keith Hartley snagged a foul ball right before it could land in the glove of Dodgers first baseman Adrian Gonzalez, it resulted in a video review -- and an out.
But what made this most recent Wrigley Field fan interference incident particularly notable was that Hartley caught the ball with his right hand -- while feeding his 7-month-old son, Isaac, in his left arm. (For the record, ESPN suggests you do not attempt this. Ever.)
Major League ... Whiffle Ball? (Oct. 23, 2011)
A Rangers fan was ejected during Game 3 of the 2011 World Series when he just couldn't keep himself from tossing a whiffle ball at Cardinals left fielder Matt Holliday as he moved to field a Nelson Cruz fly ball in the seventh inning.
Fortunately the ball didn't distract Holliday, who made the play. It also did nothing to help the Rangers, who were crushed 16-7 and would lose the Fall Classic in a seven-game thriller.
The Ichiro imposter (Aug. 2, 2011)
Ichiro Suzuki getting booed at Safeco Field? Not likely. An Ichiro Suzuki look-alike getting booed at Safeco Field? Well, that's a different story. When impersonator Kenta Imamura -- dressed like Ichiro, not only in full uniform but even carrying his signature bat and sporting similar facial hair -- grabbed a Dustin Ackley grounder as it bounced fair down the first-base line and ran along the first row of seats in foul territory, he heard it from a Mariners crowd that saw it as an easy triple.
It all turned out well in the end, though, as the umpires convened and indeed ruled the hit a triple instead of a ground-rule double.
Blondes in the bleachers (June 1, 2007)
There are a million and one examples of fans expressing themselves with signs, chants, heckles, you name it. When it comes to Alex Rodriguez and other players tainted by performance-enhancing drugs, we've seen enough asterisk posters to no longer consider them much of a novelty.
Still, we do have to credit Fenway Park fans for their creativity, when they wore masks to taunt A-Rod after a tabloid report of the then-married Yankees slugger leaving a Toronto strip club with a buxom blonde.
Legend of the fall (Aug. 9, 2005)
When 18-year-old Scott Harper jumped 40 feet from the upper deck of the old Yankee Stadium onto the screen behind home plate, to prove to his friends it could hold his weight, it was no laughing matter -- he ended up being sentenced to three years' probation for the stunt.
Still, it did elicit a classic George Steinbrenner quote after the Yankees lost the game 2-1 to the White Sox: "That was the only exciting thing that happened today."
The Bartman game (Oct. 14, 2003)
If you're looking to make the case that the Cubs are cursed, Steve Bartman could very well be Exhibit A. The headphones-wearing lifelong Cubs fan got in the way of a potential catch by Moises Alou in the eighth inning of Game 6 of the 2003 NLCS. The Marlins would go on to score eight times that inning, tie the series at three games, and win Game 7 the very next night.
Bartman? He's now the most infamous fan in Wrigley Field's long, tortured history.
The Jeffrey Maier game (Oct. 9, 1996)
The late-1990s Yankees dynasty -- and the legendary career of the Derek Jeter -- got a little boost from Jeffrey Maier in Game 1 of the 1996 ALCS. The 12-year-old Yankees fan grabbed what looked like a catchable ball from the grasp of Orioles right fielder Tony Tarasco. Instead of a fan-interference call, Derek Jeter was credited with a home run, a solo shot that tied the score in the eighth.
The Yankees would win 5-4 in 11 and take the series in five, en route to their first World Series title since 1978.
The Kissing Bandit (circa 1970s/80s)
Morganna Roberts' career as an on-field vixen began with a dare. After her friends challenged her, she ran onto the field in Cincinnati and planted a kiss on Pete Rose. She continued the practice on and off for a few decades before officially retiring in 1999.
Along the way, she stole a kiss from dozens of athletes in multiple sports, perhaps most famously hugging and kissing George Brett during the 1979 All-Star Game at the Kingdome in Seattle.
Disco demolition night (July 12, 1979)
Comiskey Park turned into a riot zone after arguably the most notorious promotional event in sports history. Between games of what should have been a doubleheader, Chicago disc jockey Steve Dahl took disco records that fans had brought to the stadium and exploded them in center field. An already rowdy crowd went wild, storming the field, ripping it apart, climbing the foul poles, you name it.
The White Sox were forced to forfeit Game 2 because the field was unplayable.
Stormin' the stadium (Oct. 14, 1976)
During a wild time in the Bronx, Chris Chambliss ended the ALCS with a ninth-inning, game-winning home run in Game 5, eliminating the Royals and sending the Yankees to their first World Series in more than a decade. The stadium crowd went berserk, storming the field. Chambliss, tripped at second base and completely swarmed by fans by the time he approached third, ran directly to the clubhouse from there.
Worried that he still needed to touch home, he later reemerged, though by then home plate had been stolen.
Still, he put his foot on the spot where it had once been, just to be, um, safe.
Making history with Hank (April 8, 1974)
Britt Gaston and Cliff Courtenay saw history in Atlanta when Hank Aaron hit his 715th home run, surpassing Babe Ruth's mark. But just seeing it wasn't enough, apparently, for the two 17-year-olds.
The pair jumped onto the field and caught up with Aaron as he rounded second base, gave him some encouragement -- and then raced off to jail.