sentences:  In 1975, the year before Clark's hiring, the American League ruled umpires could use the outside protector or the National League standard inside protector, invented in the 1910s by another Hall of Fame umpire, Bill Klem.In 1977, the AL ruled all incoming umpires had to use the inside protector, an edict which affected new hires Steve Palermo and Durwood Merrill.Umpires active prior to 1977 using the outside (aka "balloon") protector could continue to use it until they retired or switched to the inside protector.