PEORIA, Ariz. — A day that began with another step forward for Sung-Mun Song ended with him jogging off the field having experienced “tightness” in his right oblique.

Padres manager Craig Stammen called the move to take Song out “precautionary.” But the fact Song felt something in the same area as the oblique injury he suffered while hitting in January in Korea will likely cause the Padres to be careful about bringing him back.

“We’ll see what it’s like when the trainers get ahold of him and interpret it,” Stammen said. “Hopefully it’s nothing big, but we’ll see.”

While Song said he felt healthy upon arriving in Arizona, the team slow-played his start to spring training. Oblique injuries are notorious for lingering.

It was perhaps a good sign that Song was able to jog off the field while departing after playing shortstop in the second inning.

He had in the top of the second yanked the first pitch of his first at-bat 430 feet and over the bullpen beyond right field for his first home run in a Padres uniform. The blast came off a 95 mph fastball from veteran right-hander Luis Castillo.

Song, who had just one ball hit to him in his first professional start at shortstop, struck out his second time up, also in the Padres’ 12-run second inning.

“I can’t speak on if it was one actual swing or moment,” Stammen said, “or if it was just kind of gradual, like he was tired, running the bases a lot.”

Song, who was signed in the offseason to a four-year, $15 million deal after nine seasons in the KBO, began the spring 0-for-5 but has four hits and two walks in his past 13 plate appearances.

Waldron back to mound

Matt Waldron pitched in the bullpen Thursday, his first time on the mound in nearly two weeks.

Waldron began the spring as part of the competition for a rotation spot but will likely start the season on the injured list after missing time following a procedure to alleviate an infection.

Provided he remains healthy, the 29-year-old right-hander will not be able to be stashed on the IL for long, which will bring up a decision for the Padres. Waldron is out of options and, once active, must be placed on the major league roster or be made available to teams via waivers.

Adam returns

Relief pitcher Jason Adam returned to camp and will pitch a simulated inning on Friday.

He threw a bullpen while in San Diego this week for the birth of his fifth daughter and said he remains on track to be ready for opening day.

Adam, who had surgery to repair a ruptured quad tendon in September, has been pitching without hindrance for three months. The Padres, however, are slow-playing his defensive work, which requires more sudden and unexpected movement.

Transactions

The Padres reassigned right-handers Sean Boyle, Evan Fitterer, Francis Peña and Ethan Routzahn, infielders Marcos Castanon and Romeo Sanabria, infielder/outfielder Clay Dungan and catcher Brendan Durfee to minor league camp. They also optioned righty Miguel Mendez to Double-A San Antonio.

With those moves, their second round of cuts, the Padres have 59 players in major league camp.