I
looked up this popular game from my childhood and was astonished not to find it
on Google. It was simply not there! Eventually I found this on Wikipedia under Mumbl[et]y
Peg:
In the variant known as "Stretch", the object of the game is to make
the other player fall over from having to spread his legs too far apart. The
players begin facing each other some distance apart with their own heels and
toes touching, and take turns attempting to stick their knives in the ground
outboard of the other player's feet. If the knife sticks, the other player must
move his foot out to where the knife stuck while keeping the other foot in
place, provided the distance between foot and knife is about twelve inches or
less. Play continues until one player falls or is unable to make the required
stretch. (And yes - most schoolkids did carry a pocket knife.)