Humour me. I am writing this fanpost without an encyclopaedic knowledge of cricket (though it's a good deal greater than my "knowledge" of baseball, a sport I've been following since 1997 but only since April 2007 with any semblance of understanding), but with a conviction that baseball fans - some baseball fans, anyway, the slightly geeky ones with suspiciously too much time on their hands, a bit like myself - will be intrigued by the differences between their great sport and its venerable parent (no doubt Wikipedia would ask me to prove this assertion, but whether it's a direct lineage I don't know, but clearly they both evolved from the same concept. And I don't remember cricket ever appearing in any Jane Austen).
So, I'll start with the assumption that most of you have a vague idea that some dude throws a ball at another dude who tries to hit it with a piece of wood and score runs...
It's 11 versus 11. The game takes many forms, from 20/20 (in which each side bowls 20 overs (6 balls) at the other, and whoever scores the most runs wins) to a five-day match (where both teams play two innings - where an innings (note the "s" even in the singular) last as long as it takes to get 10 of the 11 batsmen out). But the rules are largely the same, bar a few nuances relating to fielding positions.
The game takes place on a wicket (meaning #1 - a strip of dry, rolled, very flat grass 66 feet long and maybe 8 feet wide roughly in the middle of the field). Two batsmen, holding blades of willow 2-3lbs in weight, are on the field at any one point - one facing the bowler, one at the bowlers end, ready to run to the batting end when the batting batsman hits and chooses to run. The bowler bowls a hard leather ball, with a considerable raised seam around the middle, to the batsman using a windmill overarm action; speeds are between 50mph for spinners - bowlers who can make the ball change direction when it bounces in front of the batsmen - to 100mph for the fastest fast bowlers.
The batsman doesn't have to run if he hits the ball - if he does so, the fielding team can get him out by hitting the wicket (meaning #2 - the three sticks (stumps) with two small sticks (bails) on top, which the batsmen is trying to protect) with the ball before the either batsmen reaches his crease - the line 3 feet in front of the wicket (meaning #2), so often when he hits he realises he would be easily run out thusly, so he stays put (occasionally the non-batting batsman will run when he shouldn't, often leading to a wicket (meaning #3 - when a batsman is out). If the bowler bowls the ball wide of the batting crease, or oversteps his crease when releasing the ball, then the batting team is awarded an extra run and the ball is bowled again.
The captain of the fielding team can place his fielders wherever he wants on the field, with the exception of the bowler (obviously) and the wicketkeeper, who performs the catcher's role (though without calling the balls bowled like the catcher does with pitches). The fielding positions can change radically depending on how aggressive the batting team are, or depending on the strengths and weaknesses of individual batsmen.
The batsman's aim, as stated already, is to score runs without getting out - once he's out, that's his part in the innings (singular) over. He can score in two ways: by hitting the ball and literally running to the other end of the wicket (meaning #1) while his co-batsman does the same, he can score as many runs as he can fit in before the ball is thrown back by the fielders - usually 1 or 2, occasionally 3. He can also score 4 runs by hitting the ball to the boundary (the rope at the edge of the field that deliniates the limits of the field), or 6 runs by hitting it over the boundary without it bouncing beforehand (the home run equivalent - only a few sixes are scored in the average innings).
The bowler's aim is to get the batsmen out. He can do this a number of ways (I think there are ten in total but a few are very esoteric), the main ones of which are:
* bowled - the ball passes the batsman (or the batsman knocks it down, or nicks it with his bat) and hits the wicket (meaning #2)
* caught - the batsman hits it and a fielder (incl. the bowler) catches it before it bounces
* leg before wicket - the ball hits the batsman in a defined area - predominantly the pads covering the legs up to mid-thigh - when it would have otherwise hit the wicket
* hit wicket - when the batsman, in the process of hitting, hits the wicket behind him and dislodges the bails
* stumped - when the ball passes the batsman and is caught by the wicketkeeper, who knocks the bails off while the batsman is in front of his crease. If the batsman remains within his crease he's safe.
* run out - when the batsmen are running and a throw from a fielder, or a stumping from the wicketkeeper, knocks off the bails before the batsman gets to the crease
There are usually 5 or 6 specialist batsmen, 4 or 5 specialist bowlers, and 1 wicketkeeper in the eleven. The specialist batsmen will bat first, the logic being they would be wasted at the tail end of the innings where the lesser players may quickly get out. A player who can both bat and bowl well is called an all-rounder - they'll often bat at 6 or 7 in the order, and tend to be very aggressive batsmen - by this point, the only remaining batsmen are the weak specialist bowlers, so any specialist batsmen still in needs to try and up their scoring rate.
This scoring rate tends to be 3 or 4 runs an over (6 balls) in a test match, 5 or 6 runs an over in a 50-over match (or "one-dayer", where both sides have one innings of 50 overs each - it last about 7 or 8 hours), and up to 10-12 runs an over in 20/20. The latter is a very recent invention, aimed towards making cricket more exciting, and isn't popular with a lot of the old guard, who see it (rightly) as a slugfest with almost all the tactical nuances of the game no longer relevant.
Winning a game in 20/20 or one day cricket is fairly straightforward - the games are designed to conclude in a result, so even in adverse weather conditions (it's not possible to play cricket in rain as it becomes too unsafe), the lenght of the innings is adjusted to ensure play to a conclusion. In a test match or other five-day match, this isn't the case - they can make up a certain number of overs lost to bad weather by extending each day's play, but for the most part, time lost is lost for good. So a lot of five-day matches end in draws, which occur when the team batting the fourth and final inning neither overtake the score of their opponents and win, or lose ten of their wickets (the innings ends when only one batsman is left) before reaching their rival's score and lose. Often, one team can be hugely on top, and would no doubt achieve an emphatic win if the game went on longer - in these circumstances, fighting for a draw can be the only option for the struggling team and in itself it's a bit of an artform, albeit quite a negative one.
It is also possible to tie a cricket game, but considering both teams usually score several hundred runs each, it doesn't happen very often.
Cricketers don't tend to have a set physiology - fast bowlers are often tall, as it's advantageous to be able to release the ball when they bowl from high up. But that's about it - I don't think there is a preferable shape for batsmen, though obviously power is a major factor so you don't want to be too weedy. Stamina is a must, as lapses of concentration can be fatal, especially when batting or fielding (it's a terrible crime to drop a catch that would get out a top batsman when he's scored half a dozen runs, only for him to reach his century - 100 runs, the statistical milestone of a great innings for a batsman). Like baseball, the actions involved, in particular with fast bowling, can punish the player's arm a great deal, and you seldom see a fast bowler at the top of the game beyond his early thirties. Top batsmen can reach 40, and spin bowlers, who seldom do more than jog a few paces and twirl their arm, very occasionally play at the top level until their 50s if they are fit enough.
Like baseball, cricket is a game of statistics, although not in nearly so much depth. Players' places in the record books come down to their batting and bowling averages - the world's best batsmen (with one exception) score 55-65 runs per innings, and the world best bowlers concede around 20 runs for every wicket they take. The exception I just mentioned is, without a shadow of a doubt, the best batsman ever to play the game, the Autralian legend Sir Donald Bradman, whose test match (international games, the highest form of cricket) batting average, over a long and distinguished career, was a staggering 99.94 runs per game. Indeed, in his last ever test, Bradman needed just four runs to average 100 (an appropriate baseball comparison would be a career batting average of .500, maybe); he was bowled for a duck (the term used when a batsman loses his wicket without scorting a single run).
So that's just about it as an introduction. If anyone's still reading, please comment and ask questions and I'll be very happy to try and answer