And, if the ball is deflected by someone else, it's quite impossible to react. A line shot into the crowd isn't going to be caught cleanly by anyone without a glove, it's going to be deflected so really it's a fantasy to think people can fend balls off through diligent attention to play.
the other thing is, in a crowd, it is difficult to bail out. You have to move up to get past the armrest, and if you simply try to duck you are limited going forward and still are exposed to sinking liners. The most crowded areas are in prime foul ball territory. New stadia were built with much less foul ball territory than the old, circular multi-purpose parks like the Oakland Coliseum and RFK; in a sense, parks built in the last 25 years are designed to have fouls go into the seats.
