If the outfielder dives for the ball and catches it but it rolls out is that an error or not?

Answer 1

No. According to Major League Baseball's Official Rule 10.12(a)(1), the game's official scorer should only charge an error to the fielder if he could have otherwise "handled the ball with ordinary effort." A missed diving play, such as a play in which an outfielder catches a fly ball while diving but then loses it upon hitting the ground, would not fall under the criteria of an error because it is not a play that could have been made under ordinary effort.