When Justin Smith decided that his body wouldn't let him perform up to his own lofty standards, he knew it was time to stop playing.
Smith announced Monday he is retiring after 14 seasons as one of the top defensive linemen in the NFL, dealing yet another blow to the San Francisco 49ers in a rough offseason.
"They all want you to keep playing, and I want to keep playing as well, but when you get on the bald tires, you're on the bald tires," Smith said.
One of the most durable players at one of the most physically demanding positions, Smith had been hampered the past two seasons by a bum left shoulder that he first hurt in training camp in 2013.
That shoulder absorbed the brunt of the punishment as a right defensive end going up against 300-pound linemen, and Smith did not feel up to playing another season.
"It doesn't respond like I want it to respond anymore," he said. "If you don't have the tools, you can't do the job. It's time to go."
Smith had just two sacks in the final 14 games last season as his practice time, snap count and effectiveness dwindled toward the end of the season.
Two other 49ers defensive stars have also retired this offseason in linebackers Patrick Willis and Chris Borland.