Pierce provided an explanation Friday, chalking it up to his workout regimen.
"Throughout the offseason, I tend to lift more than run. Being a nose guard, I want to be strong or whatnot. I, honestly, just mismanaged my running a little bit," Pierce said on WNSP-FM, according to ESPN's Jamison Hensley.
"At the end of the day, you expect a team leader to come back in better shape than I did. That's a mistake on my behalf I have to correct. I don't want to get into much more than that."
Pierce commended head coach John Harbaugh for being fair to him throughout the incident.