By Bruce Levine–

CHICAGO (CBS) — A walk-off win has become part of the fabric of the 2015 Cubs season.

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Starlin Castro provided the magic on Saturday night with a ninth-inning walk-off single in a 4-3 victory over the Reds. That was Chicago’s major league-leading seventh walk-off of the season.

Those heroics and a gutsy group of bullpen warriors have helped hide the fact that the starting pitching has been in a bit of a rut over the past week.

The five-man rotation has given manager Joe Maddon a total of 28 1/3 innings in the team’s last six starts. Although this is just a sample size of the work the rotation pitchers have contributed this season, there should be some concern.

“This happens at times,” Maddon said. “It can be streaky, but I am not concerned. Their innings and pitch count numbers are not that high. Nobody has been pushed to 110, 120, 125 (pitches). I don’t think it is a problem. If you run into a cycle, I expect a good cycle to show up on the other side. If they were hurt or tired, I would be more concerned.”

Kyle Hendricks began the dearth of innings pitched with five on June 6. Jon Lester then threw 4 1/3, Jake Arrieta went six, Tsuyoshi Wada threw three and Jason Hammel tossed five innings, rounding out a week of excessive outings for the overused bullpen. The relievers pitched 25 2/3 innings in those six contests, an average of 4.3 innings per game compared to the starters’ 4.7. The Cubs are 4-2 in that stretch.

The team’s bullpen leads the National League in the dubious departments of appearances and batters faced. Chicago’s bullpen has been a resilient group with a 1.44 ERA and a .177 batting average against since May 23.

It was Hendricks’ turn again on Saturday night in a national telecast on Fox. For the season, Hendricks has averaged 5.6 innings through 12 starts. The updated composite included a five-hit complete-game shutout of the Padres on May 5.

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Hendricks was good on Saturday. He allowed an opposite-field solo home run by Joey Votto in the fourth inning that was one of four hits he surrendered on 57 pitches (43 strikes).

The 25-year-old Hendricks got through five frames before thunderstorms washed away his time on the mound. After a 2-hour, 48-minute rain delay, it turned out to be a bullpen night for the Cubs once again, this time through no fault of their starting pitching.

It only took two batters faced by left-hander James Russell to see Hendricks’ five innings go for naught. Three straight hits off of Russell led to the game being tied up on a two-run home run by Eugenio Suarez. Russell had 11 straight appearances without giving up a run prior to Saturday. He now has pitched in 20 of the team’s 35 games since being promoted from Triple-A on May 5.

The upstart Cubs are five games into a stretch of 20 straight days with games. Chicago only has thrown one complete game this year, the aforementioned one by Hendricks. At this pace, the bullpen will need reinforcements soon.

After using his bullpen to an extreme of 15 innings in the last three games, Maddon was unsure if a call to the minor leagues was going to happen for more pitching Sunday.

“That is why I was delayed here (for postgame news conference),” Maddon said. “I don’t know about that (adding arms), but it’s something we may consider. We were taking a head count of who will be available (Sunday) and figure out the innings available to us.”

The always astute Maddon called off batting practice once again for the Sunday finale of the Reds series. Maddon has done this more times than not at home. He’s doing it on Sunday in order to let his exhausted players rest all day before the 7 p.m. start.

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Bruce Levine covers the Cubs and White Sox for 670 The Score and CBSChicago.com. Follow him on Twitter @MLBBruceLevine.