One reason behind the Pirates’ pitching issues early this season? They are not producing as many ground balls.

The Pirates led baseball in ground ball rate as a staff in each of the past three seasons, a ground ball-and-shift strategy that helped the club advance to three consecutive postseasons.

In each of the past three seasons, the Pirates’ staff combined for at least a 50.4 ground-ball rate.

This season? The Pirates entered Saturday with a 42.1 percent rate of balls in play being hit on the ground, ranking 23rd in baseball.

A byproduct of the ground ball decline is more balls have been hit in the air and over the fence. Entering Saturday, the Pirates had allowed at least one home run in every game since opening day.

They entered Saturday having allowed 14 home runs. Last season, they didn’t allow their 14th home run until May 5. They allowed the fewest home runs in the majors last season (110) and over the past three years.

What’s happened?

“No. 1, you bring in individuals that don’t have those skill sets, and you’re not at a point in time where you are going to try and take away and create something that is not there,” Pirates manager Clint Hurdle said. “I don’t believe Neftali (Feliz) is a ground-ball pitcher. I don’t believe (Jaun) Nicasio is a ground-ball pitcher. So we knew that going in. I think you are going to try and stay consistent with your philosophy where it fits and where it makes sense as far as the fastball, pitching inside, trying to create downhill angle.”

In 448 1⁄ 3 career innings, Nicasio has a 44.3 percent ground-ball rate.

According to PITCHf/x data, Nicasio has thrown a four-seam fastball on 67.5 percent of his career offerings, and a two-seam fastball 3.2 percent of the time. He’s throwing two-seamers at a 1.7 percent rate this season.

Feliz has a 36.5 percent ground-ball rate for his career and also leans on a four-seam fastball, which has less sink than the Pirates’ preferred pitch, the two-seam fastball.

“(The ground-ball decline) can be because we set the bar extremely high in those rates,” Hurdle said. “(We) can’t continually push them up. There might come a time where they plateau a little bit. You try and find different ways to attack, and that’s something we’re digging into.”

The Pirates led baseball in two-seam fastball usage (21.6 percent) last season, according to PITCHf/x. This season, the Pirates have fallen to 18.7 percent, ranking fifth, a subtle but perhaps significant change.

Liriano ready to pitch

Starting pitcher Francisco Liriano threw his first bullpen Saturday since having his previous start scratched because of hamstring discomfort.

Liriano said he is ready to return to the rotation after his bullpen Saturday, and he anticipates pitching Tuesday in San Diego when the Pirates begin a three-series road trip.

Hurdle said prior to Saturday’s game he was not ready to announce a firm plan for Liriano’s next start until speaking with pitching coach Ray Searage.

“Everything feels normal,” Liriano said. “I will be ready to go Tuesday.”

Liriano said the hamstring discomfort began in his last start in Cincinnati and lingered to his following bullpen session.

“I was going through my bullpen, and it just felt real tight,” Liriano said. “Just rehabbing for a couple days and doing some work with it, we decided not to throw because it felt way too tight and we didn’t want to rush it. Now everything feels great.”

Liriano is 1-0 with a 2.45 ERA through two starts.

Hurdle said he will wait to see how Liriano responds Sunday morning before making a decision on mapping out the rotation. Ryan Vogelsong replaced Liriano in the rotation, but Nicasio has experience pitching out of the bullpen, where he might better be suited as a two-pitch pitcher.

Travis Sawchik is a Tribune-Review staff writer. Reach him at tsawchik@tribweb.com or via Twitter @Sawchik_Trib.