[Stymie]

If one is not sure that his or her ball has is lost in a water hazard or outside it (i.e. in deep grass nearf the hazard) he or she is not allowed to play a provisional ball from the tee.  This is one of the least known and most arcane elements of the Rules of Golf.  I learned this (to my detriment) whilst playing in a USGA competition.

[Stymie]

If one is not sure that his or her ball has is lost in a water hazard or outside it (i.e. in deep grass nearf the hazard) he or she is not allowed to play a provisional ball from the tee.  This is one of the least known and most arcane elements of the Rules of Golf.  I learned this (to my detriment) whilst playing in a USGA competition.