There are seven ballparks in the mushroom kingdom, and each have their own quirks and distractions as well as a minigame. This page will describe each ball park and how to avoid falling into the traps at each one.
Mario Stadium
Mario Stadium is straight up baseball on a beach somewhere in the Mushroom Kingdom. No obstacles, distractions, or anything else you'll find at other ballparks. Turn off star skills and you'll have regular baseball. But, honestly, what's the fun in that?
Mario Stadium Minigame: Bob-omb Derby
Bob-omb Derby is as simple of a minigame as you can get. It's basically a home run derby with bob-ombs instead of baseballs. When the bob-ombs reach the outfield, they explode in fireworks for everyone in the empty stadium to see. As long as you can get the timing down, you shouldn't have any trouble with this. You can get bonuses in two ways: By hitting a big bob-omb (200 pts.) or by hitting two or more bob-ombs in a row (+15 for 2, 30 for 3, 45 for 4, and so on).
Peach Gardens
Peach has converted her courtyard into a baseball field. Unfortunately, this means that the center-field wall is the actual castle, so don't expect to hit any home runs in that direction. In fact, don't expect to hit any home runs at all, because this ball park has some of the highest walls in the game. There are two special features for you to worry about here; there are hedges surrounding the infield which temporarily conceal the ball, and there are floating blocks in the air inside the stadium. The hedges aren't a real threat; they hardly even slow down the ball. But if it gets stuck in there it's like trying to find the whiffle ball after you hit into the neighbor's prized shrubbery. The blocks are the real thing you have to worry about. There are three blocks: The bricks have stars inside of them, the solid gold blocks just act as an obstacle, and the white musical note blocks bounce the ball farther in the direction it's heading. Bouncing a ball of the musical note blocks is one of the only ways to get a home run here. Also be warned that Peach's team has mastered fielding balls of the blocks, so try not to hit too many when in challenge mode.
Peach Garden Minigame: Wall Ball
Wall Ball is the sole pitching mini game in MSB. The object is to charge up your pitch so that it goes through the musical note or "bingo" block but no farther. This game takes a little practice getting used to, and the Toads will show no mercy as you try to get the hang of it. If the first block is the bingo block, don't charge up at all or very little if you have to. If the last one is the bingo block, try to get a "NICE!" pitch. The rest are in between at different intervals, and every pitcher has to charge up more or less depending on how hard they throw.
Wario Palace
Wario Palace is Wario's desert ballpark, complete with star shaped sand dunes (that give you a star when you hit them) and gold plated statues that look just like Wario, even though he was certainly too modest to have them put in himself. He was probably so polite he didn't even argue when someone suggested it. Anyway, the two things you have to worry about here is the sandstorms and the chain chomps. The sandstorms are activated by hitting the ball in the vicinity of the floating birds in left and right field. The ball will spin around inside for a moment and will land either on the field just beyond second base or on the chain chomp in the corner of the park. The chain chomps seem to enjoy knocking around the ball if it gets close enough, even if somebody's holding it. This means you have to get your throws off fast or else your left or right fielder could get knocked out. You are also in danger of a double-whammy concerning the sandstorms and the chain chomps: If the chain chomps are awake and the ball gets hit into the sandstorm, it may go directly at the chain chomp, who will knock it into fair territory. If you don't catch it when it lands, the runner(s) will already be somewhere between second and home and will probably score a few runs before you can get the ball in. It's crazy, but that's what Mario is all about.
Wario Palace Minigame: Chain Chomp Sprint
The chain chomps at Wario Palace don't always stay in the corner. Sometimes they hang out at the pitcher's mound while the characters try to collect gems. And that's the basis for chain chomp sprint. You and three other characters run around the bases trying to collect gems. (No, you don't get bonus points for scoring a run) When the chain chomp wakes up, you have to freeze or else it will knock you out and you will lose half your gems. The controls for this game are just like normal baseball. Press 
to run forward, or you can do it backwards if you feel like it by pressing 
as you get started. You can change directions at any time by pressing the alternate button twice as you run the bases, and to stop you just need to tap it once. Luckily, the Magikoopas aren't used to being faced down by an excited chain chomp, so they get knocked around 1-2 times a game.
Yoshi Park
Yoshi Park has only one thing to worry about, the Piranha Plants. They've taken over the field and when a ball comes near them they pop out and try to catch it. Touch a Piranha Plant and you get knocked around for a bit, so if you see one of them near the drop spot, don't even think about trying to catch the ball. The only way you can catch it before they get there is with a Super Jump technique. If the Piranha Plant gets the ball first, it will hold it a few seconds and then spit it out. It will always rotate a bit before spitting it out, so to catch it (Yes, even after all that you can still catch it for an out) just stand a few feet away from the plant. (Un)fortunately, sometimes the plants at the wall will spit it out over the fence for a home run, but that's part of the game. One more thing: the Yellow Piranha Plants won't catch the ball; instead, they'll get hit by it and give up a team star to the batting team.
Yoshi Park Minigame: Piranha Panic
This game can get annoying at times, but once you get the hang of it it's pretty easy to win. There are three piranha plants at first, second, and third base. Your job is to throw yoshi eggs of a corresponding color at them. For example, you would throw a blue egg at a blue piranha plant. Unfortunately, there are four colors of eggs and only three plants out at a given moment. If you come across and egg that doesn't work, you can either wait for the right plant to come out or just throw it one of them anyway. If you throw the wrong colored egg at a plant, it will shoot a fireball at you. By holding the control stick down (
) you can avoid the fireballs. The best plant to throw "rotten" eggs at is the middle one, since its fireballs are easier to time and avoid.
At certain times throughout the game, all the plants will duck out of sight and one giant purple one will show up in the middle. At this point, throw all your eggs at him, since he spits out fireballs at everyone at timed intervals, even if they don't throw any eggs. You can get lots of points this way. Also, sometimes you will get bob-ombs instead of eggs. These are like wild cards. You can throw them at any plant, or at an opponent by throwing it like you would to home plate.