The veteran third baseman had gotten off to a .115/.233/.135 start to the season. With the emergence of Christian Villanueva, Headley's playing time was limited almost exclusively to pinch-hit at-bats.
"He got very limited opportunity, and it just got to the point where it was probably best for everybody involved to go ahead and make that change," said Padres manager Andy Green. "Nothing but gratitude for the way he went about his job and the professionalism he showed every day."
When a player's contract is designated for assignment -- often abbreviated "DFA" -- that player is immediately removed from his club's 40-man roster, and 25-man roster if he was on that as well. Within seven days of the transaction (it was previously 10 days), the player must either be traded, released or placed on irrevocable outright waivers.
The Padres acquired Headley in a December trade with the Yankees that also landed them Bryan Mitchell. They remain on the hook for the remainder of Headley's $13 million salary in 2018, unless he is claimed off waivers by another club -- which is unlikely.
In 12 big league seasons, Headley batted .263/.342/.399 with 130 homers. His 2012 campaign -- in which he led the National League with 115 RBIs -- is one of the best by a Padres hitter in recent memory. His 19.2 fWAR ranks seventh in franchise history.
"He was a pro all the way through," Green said.
Headley was dealt to the Yankees prior to the 2014 non-waiver Trade Deadline, when he was a pending free agent. He re-upped with New York for four years before he was dealt back to San Diego this past December. Many in baseball viewed that move as a salary dump by the Yankees. The Padres took on Headley's contract largely because they envisioned big things for Mitchell -- who has mostly struggled thus far.
The future is uncertain for Headley, who turned 34 on Wednesday. He posted a .273/.352/.406 slash line as recently as last season and played regularly in the Yankees postseason run. But his woeful start to the '18 campaign left him without any playing time in San Diego.
"We were invested in seeing Christian play on a pretty consistent basis," Green said of Villanueva, the reigning NL Rookie of the Month. "Christian obviously took that opportunity in April and ran with it."
The lefty-hitting Spangenberg figures to provide much more versatility off the bench. He can play third, second and left field, and he's expected to start against certain right-handers. Spangenberg batted .196/.237/.357 in 21 games for the Padres this season before he was optioned to El Paso in late April.
"I could see him over at second base at times, some real double-switch possibilities," Green said. "His versatility has been missed, and his bat. When he gets going, he can hit. Hopefully we can keep him in a really good rhythm here."
Spangenberg batted .293/.328/.534 in 13 games at Triple-A.