The key was the betrayal of Sir William Stanley, whose forces attacked the Yorkist flank, causing them to melt away.  
This battle ended with the loser asking for death and having his wish granted by being unhorsed and killed in a bog.  Early on August 22nd, the eventual losing army gained a superior position on Ambien Hill, but the tide turned when John Howard was killed in the initial skirmish.  One army had landed at Milford Haven and marched toward the other, which was near Leicester [lester].  The key was the betrayal of Sir William Stanley, whose forces attacked the Yorkist flank, causing them to melt away.  FTP, identify this 1485 victory for Henry Tudor, which brought the Wars of the Roses to an end.
This battle ended with the loser asking for death and having his wish granted by being unhorsed and killed in a bog.  
Battle of Bosworth Field