Do yo mean play at all, play professionally or play at the highest level?

Hardest to do at all would be something like cliff diving that requires a certain skill and specialized equipment or a specialized location.  Anyone can go in their back yard and play a pick up game of baseball.

Play professionally at all really depends on the number of jobs available compared to number of people who play.  In that case, the hardest would be something like softball, where thousands of women play at the collegiate level but only a couple can actually make a living at it.

But what I assume you mean is what sport is the hardest to become a great player or champion.  Baseball is up there in this case, but I'd have to say the toughest is:

Boxing.

I think we're all aware of the kinds of training boxers go through.  On top of that, great fighters posses tremendous skill, learning to throw certain punches and combinations without dropping their guard and getting clocked.  Then there is the almost certainty that you will get repeatedly hit in the face and gut by an opponent who, according to the rules of the game, is trying to give you a concussion.  And of course, there is the possibility of death.

Did I mention that in order to become a champion, you (usually) have to convince the current champion to fight you?  If he declines, there is little you can do.

Now it isn't difficult to become a professional boxer.  Anyone can enter the ring, get the crap kicked out of themselves for a round or two, collect three hundred dollars and then legitimately call themselves a professional boxer.

But to be a champion?  That requires a level of skill and athleticism that few athletes in other sports even come close to approaching.

Go on.  I dare you to tell Floyd Mayweather that his job is less difficult than Alex Rodriguez's.  I can guarantee you wouldn't like his response.  Of course, this is Mayweather I'm talking about here, so his response would probably be to never shut up until your ears exploded. :-)

There's no doubt that baseball is the hardest game to play, requires the widest range of skills. It may be true that sports like basketball or boxing or football, given the fact that they are more physically demanding, appear harder to play, but no sport requires as large a skillset as baseball. And it can be played well at the professional level by people of many different sizes and shapes, something that can't be said for any other sport.

And I have to say from what I've play and what I have seen on the professional level, it is a pretty close call between Basketball and Hockey.

I'm not a huge fight fan, but I do watch occasionally, and I've always considered boxing etc. as the purest form of sport. Essentially, every athletic skill is required in these sports, from endurance, to power, to agility, to strategy, to coordination, to reaction time etc. all while interacting in an altered state of conscious from having your bell rung.

first let me say each sport has it's difficult skills that only extraordinary athletic people can accomplish successfully. Hitting a baseball is certainly one of them. Football has the physicality and the teamwork of eleven players at a time. Some of you may know me as a basketball coach. The one point I make defending the difficulty of basketball is imagine pitching while someone is guarding you.....or hitting. This is what makes basketball so difficult. Like I said, each sport is tough. What you all have missed with baseball is that there are little games within games, the situational parts of the game that players have to react to so quickly. Take the master (Maddux) setting up pitches games in advance, the hit and run and the player movement that sets it up and the knowlege that must be reactional in each situation. Baseball is tough, but so is each sport. Just don't send DLee us to guard me when I have to bat vs. Billy Wagner in the 9th inning!

at the highest level. think about it while you watch the masters.

Try racing sailboats sometime.  Not only do you have to be in great physical shape, you have to be intelligent, too.

Within the context of the major professional sports, I'd have to agree with those who believe baseball requires the widest range of difficult skills while basketball requires the greatest physical conditioning.  It wasn't surprising that as great an athlete Michael Jordan was, he couldn't get above AA ball.

Is there another sport in which a 70% failure rate can get you to the Hall of Fame?  No.  Lifetime .300+ hitters go to Cooperstown because squarely hitting a round ball with a round bat is the most difficult thing to do consistently in all of sports.  And hitting for average is only one of the many skills required to play baseball at the highest level.

ALL other sports are inferior to BASEBALL.

CUBS BASEBALL is who we are and why we BLEED CUBBIE BLUE !!