Like committing to a sprint target. And literally doing everything to fulfill it. Like not waiting for a manager to step in and ask for overtime and weekend shifts. Remember? Scrum teams take all the necessary steps themselves. Always!
Isn't the entire point of scrum to enforce a sustainable pace of development? One that doesn't require heroics like having programmers come in on nights and weekends to finish? The entire point of tracking time and making burndown charts is so that you can avoid taking on too much work. If your team doesn't have the ability to push back on the requirements and say, "Hey, this is too much, we need to push features X, Y, and Z into the next sprint," you're not really doing scrum. You're doing kabuki-scrum, which is usually just waterfall with all the meetings relabeled.