The bowler reaches his delivery stride by means of a "run-up", although some bowlers with a very slow delivery take no more than a couple of steps before bowling. A fast bowler needs momentum and takes quite a long run-up, running very fast as he does so.
The fastest bowlers can deliver the ball at a speed of over 90 miles per hour (140 km/h) and they sometimes rely on sheer speed to try and defeat the batsman, who is forced to react very quickly. Other fast bowlers rely on a mixture of speed and guile. Some fast bowlers make use of the seam of the ball so that it "curves" or "swings" in flight. This type of delivery can deceive a batsman into mistiming his shot so that the ball touches the edge of the bat and can then be "caught behind" by the wicketkeeper or a slip fielder.
At the other end of the bowling scale is the "spinner" who bowls at a relatively slow pace and relies entirely on guile to deceive the batsman. A spinner will often "buy his wicket" by "tossing one up" (in a slower, higher parabolic path) to lure the batsman into making a poor shot. The batsman has to be very wary of such deliveries as they are often "flighted" or spun so that the ball will not behave quite as he expects and he could be "trapped" into getting himself out.
In between the pacemen and the spinners are the "medium pacers" who rely on persistent accuracy to try and contain the rate of scoring and wear down the batsman's concentration.
All bowlers are classified according to their looks or style. The classifications, as with much cricket terminology, can be very confusing. Hence, a bowler could be classified as LF, meaning he is a left arm fast bowler; or as LBG, meaning he is a right arm spin bowler who bowls deliveries that are called a "leg break" and a "Googly".
During the bowling action the elbow may be held at any angle and may bend further, but may not straighten out. If the elbow straightens illegally then the square-leg umpire may call no-ball: this is known as "throwing" or "chucking", and can be difficult to detect. The current laws allow a bowler to straighten his arm 15 degrees or less.