Understanding Yellow Lines on Baseball Fields: Home Run Rules Explained

Question
What is the purpose of a yellow line on outfield fences? I think I have seen balls hit the yellow line, bounce back on the field of play and be called a home run.  I always thought a ball must leave the field of play to be a home run, unless striking the foul pole.

Answer
Jerry,

Only certain fields have the yellow line, but in most cases, if the ball hits above the line, it is ruled a home run.  It depends on the ground rules for that particular stadium.

Typically they were put into place to make the calls easier for the umpires.  I'm not sure they do this, but that was the original thinking.

Again - how the line is treated depends on the ground rules set in that particular stadium.

Hope this helps!

Brian