Trivia/fun fact (easy)
 

Name the only two players who, over a period of at least a couple of years, traded off being the all time leader in a major statistical category.

Not talking early 19th century stuff.

Rose and Yaz in Games Played?

Carlton and Ryan for strikeouts?

This was my guess as well.

As a huge fan of both pitchers, but especially Ryan, I followed their battle closely, keeping a paper log of all their outings and strikeouts.

Steve

According to WIkipedia there were 19 lead changes before Ryan finally took the lead for good.