What is the ruling when a baseball hits the yellow part and comes back in?

Answer 1

The ball must clear the fence or hit above the yellow line. If the ball hits the line and comes back into play then it is a live ball (assuming it wasnt interfered with by a fan) just like any other ball that hits off the wall. In stadiums like Chase Field in Arizona that have a line on their wall in centerfield, if the ball hits above that line then it is a homerun, below the line is just a hit off the wall. Same with Fenway Park in Boston and where the "Green Monster" meets the wall in centerfield