The Field of Play
A Baseball field can be divided into three sections:- the infield, the outfield and foul territory. No two Baseball fields are exactly the same.
The infield should be identical from one stadium to the next. The infield is a 90 ft square (though it's called a diamond), and has a base (first base, second base, third base and home base) at each corner. Each base is 90 feet away from the next. In the middle of the diamond, 60.5 feet away from home plate is the pitcher's mound.
Home base is a five sided slab of whitened rubber, 17 inches wide and 17 inches long with two corners removed, whilst the first, second and third base bags are 15 inches square. The pitcher's mound is (currently) ten inches above home plate, but this height has been varied in the past to favour pitchers (higher mounds) or hitters (lower mounds).
The base paths (the spaces between the bases along which runners run, or slide) are made up of dirt, which may be swept periodically during the game by the "grounds-crew" between innings.
The outfield should be at least 250 ft away from home plate, though it's generally considered 325 ft is the minimum along the foul lines, and 400 ft to center field. The outfield is normally surrounded by a wall, but there is no uniformity with outfields and their walls. Some have high walls, some have short walls, some walls have turns and nooks and crannies, and one even has a hill! At the end of each "foul line" (which extend from the first and third base lines), there's a huge "foul pole" to show which long hits are fair and which are foul. If a ball hits the foul pole, it's fair (so logically it would be called a "fair pole", but that's tradition).
The last three or four feet of the outfield is generally made up of dirt as well, known as the "warning track". Quite simply it's there to warn an outfielder racing after a fly ball that something big and solid (though often nowadays, padded) is very close to him.
The distance of the outfield walls is very significant for any team, particularly a home team. If the walls are close, then home run hitting is much easier whereas long walls make it more difficult (and a team is more likely to be built on "single hitters" and "speed") to steal bases and so forth. If the wall in right field is shorter than in left field, it favours left handed hitters (who pull to right field) and so forth. Teams are often built to suit the dimensions of their home field.
Foul Territory is the space outside of the first and third base lines in which a hit ball isn't fair, but can still be caught by a hustling fielder. In some stadiums the fans and seats are very tight to the foul lines, and there isn't much scope for getting outs in fair territory - in others there is much more space, and the pitching team may well get "easy outs" on fly balls in foul territory.
If a ball is hit in fair territory, but then rolls foul, it's a foul ball only if if crosses into foul territory before reaching the first or third base bag or (rarely) rolls back into fair territory. If it hits first or third base, or lands in fair territory beyond either base and then rolls into foul territory, it's fair. If it rolls past the bag before going foul then it's a fair ball (but not if it doesn't land in fair territory). You'll sometimes see a fielder watching a bunted ball hoping it rolls foul (though he can still pick it up and field it, making it fair).
If a ball is touched by a fielder (or umpire) whilst it's in fair territory it becomes a fair ball (even if it rolls foul) and vice versa.
Fan interference can also be a factor in stadiums. If a fan leans over a wall and grabs a ball (preventing a fielder from catching it) then the umpire can still rule the hitter as out. However, if a fielder leans over a wall and is prevented by a fan from catching the ball, then the hitter is safe, and often an argument between the fielder and the fan will ensue.
Most stadiums now have grass fields, though during the 1970's and 1980's astroturf was quite common. This was generally quicker, provided better fielding (no awkward bounces) and caused more injuries (to ankle and knee joints). Many of the same 1970's and 1980's stadiums also featured "domed" buildings, where the games were effectively played indoors (so no weather conditions to adjust to, or worry about).
The most modern stadiums generally have grass fields, and retractable roofs, offering the best of both worlds. If it's raining, cold (or so hot and muggy it would be unbearable), the roof can be shut, but if the weather's perfect the roof can be left open. For some evening games it's even agreed that the roof will be shut at a pre-determined stage of the game (such as at the end of the third inning - so it's the same for both teams).
Pitcher's Parks/Hitters Parks
Many ballparks are referred to as "pitcher's parks" or "hitter's parks", depending on whether the stadium configuration favours one or the other.
Ideally, a pitcher would like a park with long distances to the outfield fences (making home runs harder to hit) and lots of space in foul territory (so foul balls can be caught). If the outfield fences are closer, it favours the hitters, and if the stands are close the foul lines, then those foul balls simply fall into the stands, and can't be caught.
Whether hitting or pitching is favoured, may also depend on the weather. If the wind is blowing away from the plate, home runs will carry further, whereas if it's blowing "into the park" long balls will hold up in the wind. The ball tends to travel further in hot, humid conditions.