Just to expand on Giles’s post:
You will notice that, in Test Cricket, a ball can be replaced under normal conditions after 80 overs. An over is six deliveries, so that means a Test Match cricket ball gets bowled 480 times before it is replaced.
Not only that, but unlike a baseball, a cricket ball does not generally reach the batter on the full; it bounces on the ground between the bowler (pitcher) and the batter. So, as well as getting hit by the bat, the ball also gets hit and scuffed by the ground.
A cricket ball is slightly smaller, a bit heavier, and harder than a baseball. It is made of a cork core, wound around with very tight string, and covered in leather. Unlike a baseball, the pieces of leather in a cricket ball are sewn together in a straight circumference around the ball, dividing it into two hemispheres. The two halves are held together by three rows of stitches on each side, leading to the nickname “six stitcher” for a cricket ball. Here is a picture of one. The red color is the result of dying.
When the ball is new, it is very hard, and bounces quickly off the wicket (the ground). The red shine on the ball also allows it to move through the air, in a manner similar to a curve ball in baseball. This effect can be accentuated by polishing one side of the ball. Bowlers will often spit on one side of the ball and rub that side on their trouser leg, giving it some “shine” and making it easier to move the ball through the air. Bowlers can also get movement off the wicket (known as “cut”) by bouncing the seam of the ball on the ground. If the ball bounces on the seam, it can deviate left or right quite suddenly, making life difficult for the batter.
As the ball is used, and gets older, it gets softer. The shine goes away, and the seam flattens out. But, the increasing roughness of the ball can make it susceptible to “spin.” That is, there are certain bowlers, called spinners, who make the ball spin in flight, in such a way that when the ball hits the ground, the spinning motion makes it jump to the left or to the right.
For the above reasons, the first bowlers used in a cricket match are generally fast bowlers, whose speed and ability to bounce the ball off the wicket can take advantage of the new, hard ball. By contrast, spinners are usually utilized in a cricket match when the ball gets older, because the shiny new ball often can’t get enough grip on the ground to spin very well, but the rougher old ball can get a grip and will spin much more readily.