College Football/College football
What is the purpose of the hash marks on a field that exist around the 30 and40 yard lines? Do they determine where the players must be positioned during a kickoff?
Thank you for your question. There are no field marking designed or required to establish or mandate where players are positioned during a kick off. I can assume you are asking about "X" marks on either the 35 or 40 yard lines which are optional marks some game administrators put on the Free Kick line (40 yard line under NFHS rules and 35 yard line for NCAA and NFL fields).
The purpose of the hash marks generally is for positioning of the ball not players.
You refer to Hash marks in your question. I am not sure if you are using the proper term or whether you may have viewed field that is either shared with other sports and the marking you saw is for another sport or it was a field with a marking that is not uniformed to the rule.
Hash marks are the two inbounds lines (hash marks) that are spaced are 60 feet from the sidelines on the NCAA field. These Inbound lines and short yard-line extensions shall measure 24 inches in length. . The primary purpose of the yardlines is to measure the ball's position relative to the two goal lines. The hash marks are used to roughly position the ball relative to the field's width. So, after each play, the ball's position relative to the goal lines is marked using the set of hash marks closest to where the ball came to rest at the end of the play. As background, in the 1933 two rows of hash marks were added near the center of the field at one-yard intervals on professional football fields.These hash marks were one of professional football’s first deviations from the college game: "at the end of each play, the ball would now be placed on the nearest hash mark. Prior to the 1933 rule change, all plays began where the ball was last declared dead.
This is a link to high school football field diagrams:
This a a link to NCAA Football Field diagram:
For a detailed history on NFL Hashmarks you may want to read: "A Brief History of Hash Marks" by Jackson Michael from the book The Game Before the Money See http://www.thegamebeforethemoney.com/a-brief-history-of-hash-marks/
If you have an image of the marking I may be able to better tell you their purpose if any for the game. However the marking that is optional near the area on the field you describe is likely the "X" that I discussed above.