So many times throughout the course of a game, it's where the line separating civility from grit is tiptoed -- or slid through.
Managers, coaches and an old-school mentality tell baserunners to do whatever it takes to break up a double play. Major League Baseball rules tell them an attempt at touching the bag must be made. And morality tells them not to injure a fellow ballplayer.
Most of the time, all of the above are compromised effectively. Sometimes -- as was the case in the Bronx on Thursday and in Houston on Friday -- they aren't.
And almost every time a double play is turned, an injury is a mere inch or second away for a middle infielder.
"Every time you're trying to make a double play, the runner is going to be right there, and you just have to be careful and get out of there as soon as possible," Mets shortstop Jose Reyes said. "Sometimes it's going to be tough."
It was tough for Twins rookie second baseman Tsuyoshi Nishioka on Thursday, when Nick Swisher's sweeping left leg caused a fractured fibula. And it was tough for Marlins star shortstop Hanley Ramirez on Friday, when a late charge by Bill Hall resulted in a bruised shin.
For the most part, the two slides were deemed to be clean. And in each case, the injuries weren't as bad as initially believed -- Ramirez is expected back in the lineup on Tuesday, and while Nishioka is out 4-6 weeks, he won't require surgery or a cast.
Each play, however, served as further proof of just how dangerous turning a double play can be.
"You're going to get hit at second base," said Twins manager Ron Gardenhire, primarily a shortstop but who played in 30 games as a second baseman during his five years with the Mets. "It's going to happen."
In 1994, Omar Vizquel suffered a strained MCL at the hands (or, feet) of Ivan Rodriguez. Eight months ago, Chase Utley's violent slide on New York's Ruben Tejada increased tensions between the Mets and Phillies.
Umpires will normally grant a baserunner plenty of leeway, only calling interference if he blatantly goes after the fielder and is too far away from the bag -- as was the case with Red Sox third baseman Kevin Youkilis on Sunday night. In that situation, the Yankees turned a bases-loaded DP but the umpire called Youkilis for interference and ordered the other two runners to return to second and third.
Besides those rarities, the fault usually lies with the fielder if he's unable to get out of harm's way. But they also have a job to do: complete the double play.
And therein lies the balancing act.
"Turning a double play is not easy," veteran Nationals infielder Alex Cora said. "Especially at this level."
Middle infielders basically ask for three things from a hard-charging baserunner: make sure you're within reach of the bag, keep your spikes down and don't go above the ankle. Besides that, they understand the physical nature.
"You have to break it up," Mets utility man Willie Harris said. "No matter if it's your friend or what, you have to break it up."
In the Far East, the mentality is totally different.
For middle infielders jumping to the pros from college, where the rule forces baserunners to slide directly into the bag, turning a double play is a big adjustment. But as a season-ending injury to former Rays second baseman Akinori Iwamura showed in 2009, and Nishioka's recent mishap reminded, it may be an even bigger one for those coming to the Majors from Asia.
Very few are trying to break up two there.
"They play the game very gentlemanly," said Mets skipper Terry Collins, who coached in the Far East from 2007-09.
Nishioka, several members on the Mets and Nationals said Saturday, stayed on the ground too long during Swisher's slide, which probably had more to do with habit than bravado.
In Japan, second basemen can comfortably relay a throw to first base without the danger of being flipped, and catchers simply have to plop down on their knees to effectively block the plate.
"That's just the way they play," Collins said. "I wish I had an answer for it. We tried to get them to understand the importance of sliding in, breaking up the double play and trying to help the team win, but that's not how they're taught."
In the West, professional middle infielders are taught techniques to avoid injury while turning two -- keep runners guessing on which side of the bag you'll throw from, escape quickly, know who's running, keep your left toe pointed to first base whenever possible and tumble forward on impact.
For Harris, the key has always been to arrive at the bag ahead of time, then throw from below his shoulder to force the baserunner to slide early.
If he doesn't ...
"You activate his dental plan," Harris said. "One way or the other."
Sometimes it's just that simple -- you get rid of the ball, and if the runner chooses not to get out of the way, it'll whack him in the face. But on slow rollers that result in bang-bang plays at second base, the onus is on the fielder to either elevate or navigate around the bag to avoid the incoming runner.
These days, the Phillies have built a reputation for coming in hard to break up would-be double plays -- and not just because of the one incident against the Mets last August. Back in the 1980s, Mookie Wilson recalled, it was stout third baseman Bill Madlock who put fear into the hearts of so many middle infielders.
The danger has always been there -- and it will continue to be.
"You have to try and extend innings as much as you possibly can, and that means taking a guy out sometimes," said Wilson, the former Mets center fielder and current first-base coach. "It's unfortunate that guys get injured, but that's been happening since baseball's been around. It's not something you can avoid."
Alden Gonzalez is a reporter for MLB.com. Read his columns and his blog, listen to his podcast and follow him on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.