To put it bluntly, the Pittsburgh Pirates tend to be sore losers when it comes to taking on the Chicago Cubs.

In both series the Pirates have played against the Cubs this season, the Cubs have had the upper hand. And both times, the teams appeared to be on the verge of a bench-clearing brawl.

After Pirates outfielder Starling Marte was hit by a pitch from Cubs starter Jason Hammel at PNC Park earlier in May, the Pirates retaliated by plunking Cubs utility man Ben Zobrist. The result was a shouting match between Cubs manager Joe Maddon and Pirates catcher Francisco Cervelli.

The most recent incident between the two teams took place in the fourth inning Saturday afternoon at Wrigley Field.

After running into some trouble and giving up two runs with another man on third base, reigning National League Cy Young Award winner Jake Arrieta nailed Pirates infielder Jung-ho Kang square in the back with a 92 mph fastball in the first pitch of his at bat.

This isn’t foreign behavior in baseball, where the actions of players are dominated by “unwritten rules” that have existed since baseball’s inception.

These rules include: don’t step on the chalk lines when taking the field, don’t bunt to break up a no-hitter and don’t show up the pitcher after a big hit unless you want to get hit. Those rules, while never formalized, are pretty clear and easy to follow.

But a problem arises when teams try to decipher whether a batter was hit on purpose, because there is no way to really know for sure unless the pitcher comes out and admits to intentionally pegging the batter.

As expected, the Pirates deemed Arrieta’s rare loss of control as intentional, while the Cubs vehemently denied it.

“Anytime somebody like Arrieta hits somebody, you’ve got to assume automatically that one didn’t just get away,” Pirates starter Jeff Locke told the Pittsburgh Post-Gazette after the game. “I don’t know what happened on the pitch. It got [Kang] pretty flush, though.”

The Cubs’ manager strongly disagreed, with a possible allusion to the takeout slide that injured Kang in a Cubs vs. Pirates game last September.

Maddon told the Post-Gazette that only fans expecting a fight would imagine the hit was on purpose.

“Why would we ever want to hit him based on what happened last year? That makes no sense whatsoever,” Maddon said. “There’s no dots to be connected there.”

Whether it was intentional or not, the Pirates are overreacting to the Cubs’ mistakes out of frustration, when the real way to get revenge is to beat them.

The Cubs have dominated the Pirates this season, winning five of their six meetings by an average of more than four runs per game.

The run differential between the two sides so far is +25 in favor of the Cubs. To put that in perspective, the World Series Champion Kansas City Royals had a run differential of +83 last season after playing an entire season of 162 games.

The Cubs have no reason to intentionally hit Pirates players and give them free opportunities to get back into games when they are beating them this decisively.

The magnitude of defeats for the Pirates has obviously been frustrating to the team.  Going up against the Cubs’ league-best pitching staff led by Arrieta, the reason for these defeats is pretty clear.

Instead of realizing that the real issue lies within their pitching staff, the Pirates have gotten frustrated and retaliated the old-fashioned way toward their division rivals. Accusing a better team of using dirty tricks to get ahead is ugly, even for a sport that relies on a set of unofficial guidelines fans love to watch play out. 

So far, all of the Pirates’ starting pitchers have been shaky — including the stalwarts, Gerrit Cole and Francisco Liriano.

Cole — who missed all of Spring Training and the first four games of the season due to a rib injury —  snapped back to his 2015 form while tossing eight shutout innings in a 2-1 win over the Cubs on Sunday. But the starting rotation as a whole has not been reliable.

Meanwhile, numerous bullpen collapses throughout the season have turned the staple of the franchise over the past few years into a liability.

Losing to the Cubs has not exposed Chicago as a dirty team, but rather highlighted the Pirates’ weaknesses in both the starting rotation and the bullpen.

Trading blows with the Cubs won’t help the Pirates win — solidifying an inconsistent pitching staff will.