This is a tough one. I generally agree with most of the comments that you don't want to bench players who have been with you from the beginning for someone you pick up late. With that being said though, I think it can be a little different when you're talking about attending a nationals. First of all, I don't think you ever want to go to a nationals with less than 11 players if you can avoid it. If you get into the loser's bracket of a double elimination tournament, you can end up playing as many as 6-7 games in a day or I've heard of teams playing in as many as 10+ games in two days. If someone gets sick or injured, you can't ride 9 players through this many games or, even worse, risk getting down to 8. You're better off to pick up another player whose team isn't going to nationals and trying to get more games in for everyone. Now, coaches have to be a little careful as to how they use that extra player. If you ask them to come and in essence do your team a favor, you certainly need to play them and make them feel like they're part of the team. The few times I picked up an extra player, I would usually bat them at the bottom of the order the first game they played (and I would privately explain to them why), and I let them prove themselves to the rest of the team and "earn" their way up the batting order and/or on to the field. I also made sure the new player wasn't "replacing" the same person multiple games. Almost always, the girls were great and understood, but no doubt sometimes the parents still had issues.