Stample is a word made up to cheat in scrabble. It is not currently found in any English dictionaries and is not sufficientlydifferent from trample to justify an entry.
Stample is a descriptive, almost onomatopoeic, word to describe the act of being trampled on in a stampede. Usually by a herd of elephants, bison, or water buffalo.
This word comes in handy whilst on safari, or at your local rodeo when describing accidentally falling in to the steer corrall after a few drinks.