The principle sounds simple: play with pain, but not with injury. But figuring out where the line is can be difficult.
Chacin, whose first full season was last year, and Nelson, who made the Opening Day roster for the first time this season, have suffered not only from pain but from a lack of understanding of exactly how much they were limited by their injures. There's also the player's natural urge to play through pain.
"I knew my arm wasn't good, but I was trying to pitch through it," Chacin said. "I'd never been on the DL before, even in the Minors. I've been sore before, but this was something different. I was really weak in my rotator cuff.
"I have to get strong in the rotator cuff. If I didn't do that, it could get worse and maybe I'd have to have surgery."
Nelson battled various injuries throughout his Minor League career, and often was criticized for the repeated injuries. In his first real opportunity in the Majors, human nature took over and led him to not admit how hurt he was. The final straw might have been a diving play he made Sunday in Los Angeles.
"You don't want to be on the disabled list," Nelson said. "It's nothing you want to be proud of.
"But at the same time, I'm not really helping my team or helping myself. I just need to get it back healthy. Especially hitting with my wrist, and diving and all that good stuff, this is a learning experience."
Manager Jim Tracy said especially with Chacin, he asked him if he was hurt and had athletic trainer Keith Dugger keep a close eye on him. The problem, Tracy said, is it often has to come down to the player and the knowledge of his body, which isn't always there with an inexperienced player. Tracy admitted the club needs to be more proactive with inexperienced players.
"It's not a bad thing; it's understandable," Tracy said. "A young player at times is not going to be as forthright. You have to keep forcing the issue. You want honesty.
"There are a ton of athletes during the course of the season that play through soreness, get through stiffness. But pain is a completely different thing."