SethPDX wroteWhat's a hash mark?
I only do baseball/softball, but I'm pretty sure they're called inbound lines. π
Correct, hash=inbounds lines
right from rule 1:
e. Inbounds lines βa series of hash marksβ should be 24 inches in length and 4 inches in width and shall be located 53 feet, 4 inches from and parallel with each sideline dividing the field of play longitudinally in thirds. The inbounds lines shall be marked so that each 5-yard line bisects the hash mark.
NOTES:
1. Game administration may place on the field of play, at the inbounds lines, yardline extensions that should be 24 inches in length and 4 inches in width.
...
I underlined the word parallel.
What BisonBJ is referring to are what the rule calss "yardline extensions"
The two markings are not the same.