I understand how much work the grounds keepers put in to making the grass so beautiful. However, I don't understand why they have to be such jerks about trying to keep people off the grass, especially when they are allowed to be on it.

Being my 5th appearance at a World Series I've come to expect this kind of abuse from the grounds crew. But, what I never expected was the behavior of the grounds crew when the San Francisco Giants dismissed the Tigers when they swept them in 4 straight games.
As soon as the deciding game was over, the grounds crew made a human line along the first base line in front of the Giant's clubhouse and refused to let anyone pass. Their attitude was, "You ain't goin' to celebrate on our turf!" Players, their families and the media were shoed away from the field at every opportunity. I've never seen such classless behavior from a professional sports organization.
Two years ago the San Francisco Giants became the world champions when they won Game 5 against the Texas Rangers at the Ballpark in Arlington. At no time did the Rangers organization even try to prevent the Giants from celebrating their victory.
What I've taken away from this experience is to avoid being a sore loser. Grace and dignity should be exercised, even when your team gets spanked at home.