College Football/touchback or not
can a player downing a punt be standing in the endzone and keeps the ball from breaking the plane(downs it on the 1 yard line)........Touchback or on the 1 yard line?
Thank you for your question. The key to understanding your question is that for a touchback to occur the ball must break the plane of the goal line. I assume in your question the player downing the kick is a member of the kicking team (if the player is a member of the receiving team it could be a touchback or there could be an issue of the momentum exception to a touchback, but I would need more information).
Generally, there are some things to consider when in a play situation as you describe: first touching/illegal touching (depending on the rulebook High School rules/NCAA) this is the location the kicking team first touches the kick as this becomes a spot; also the spot where the kick becomes dead by rule; and as you correctly point out whether the ball crosses the plane of the goal line.
With that said a member of the kicking team "downing a punt" (scrimmage kick) while "standing in the end zone" (beyond the goal line) keeps the ball from breaking the plane of the goal line is legal; and if the ball does not cross the goal line it remains in the field of play. The first touching spot/illegal touching spot is in the field of play. You state that the ball is "downed on the 1 yard line" I assume you mean the ball becomes dead by rule at the 1 yard line. That being the proper assumption the ball would next be put into play by the receiving team at the 1 yard line.
If ruled a touchback I suspect the covering official had a first touching or illegal touching spot on the goal line or behind he goal line. Otherwise your play situation should be at the 1 yard line.
Please know Rule 8 in both the National Federation of High School Football Rules and the NCAA rules addresses touchbacks.
I hope this answers and explains the play situation to you.