In the simplest possible terms, bowling is about getting the ball from one end of a 22-yard pitched wicket to another, with the restriction that your arm stays straight in the rotation leading up to its release. This isn't the place to enter into debates of the technicalities of the throwing laws; but at lower levels of the game there are few instances of no-ball calls for 'throws'. Suffice to say, barring your action being very suspect, you are unlikely to experience many allegations of chucking - unless you've just taken 10 for 13, in which case I'm not sure why you're reading this.
The basic biomechanics (a term used to signify the study of body movements in the name of optimising the use made from them, and minimise injury) of bowling, and indeed the basic biomechanics of propelling any object, tell us that in order to get the highest speed possible, we need to make sure that all parts of our body are working in the same direction.
If, for example, I attached two lengths of string to a tennis ball and then pulled one length in one direction whilst a friend pulled the other length in another, then the ball wouldn't move (provided we both pulled with the same force, google 'Newton's Laws' for more detail!) If, however, we both pulled in the same direction, the ball would would accelerate at the maximum possible rate (given the forces that we exerted upon it). Should we then take two steps apart, and create an angle of around 15 degrees between ourselves and the ball, the ball would still accelerate when pulled - but not to the same extent as it had before. Are you following? If not, bookmark this page, grab a tennis ball, some string, sellotape and a mate, and come back in ten minutes.
Okay? Good. Now, how to we translate our experiments with the tennis ball into getting the most speed out of our bowling actions? Well, because of the large number of moving parts in a fast bowler charging to the crease, it's difficult to line everything up into that same direction to propel the ball at its maximum speed. The two most important parts of the body to guide us in this lining-up exercise are the hips and shoulders - if you imagine two lines running through your body, one through the hips and one through the shoulders, when these are parallel with one another, then everything's pointing in just about the same direction.
There are many different angles where you can align yourself with the crease with equal validity 0 England's Andy Flintoff and Matthew Hoggard exemplify two extremes, Flintoff lining himself up in a very front-on manner, with both imaginary lines running between mid-off and mid-on, at right angles to the wicket. Hoggard, on the other hand, has a side-on action, and the imaginary lines in his body point roughly in line between the umpire at the bowler's end and the wicket-keeper. Between each end of the scale, there are myriad possible positions - called 'midway' actions in current coaching speak - Glenn McGrath is one of the many Internationals who bowl in this manner, his imaginary lines
will tend to point towards the slip cordon. Next time you're watching a video or DVD of highlights, try to pause the recording at the moment where different bowlers release the ball and ask yourself where the two lines lie.
Problems start to occur when the two lines are not parallel - not only does this mean that there isn't as much speed being generated as there could be, but more seriously greatly increases the risk of injury, especially to teenage bowlers. Think about it, if the line through your hips is pointing between mid-on and mid-off, and the line through your shoulders is pointing between umpire and 'keeper, how does your upper body move to allow this? The answer - not one for the faint of heart - is simply that the back and spine have to twist. Doing this every ball in match and practice for weeks and months on end can have a huge effect on a bowler's back; the number of bowlers with these flawed 'mixed' action is the direct reason behind the ECB's restrictions on the number of overs that under 19s may bowl.
So, why do these mixed actions occur, and what can you do to smooth them out if you realise that you or a friend have an action like this? To get back to our imaginary lines, we need to move either the hips or shoulders so that they're in line with the other. It doesn't matter which is moved, but it's generally a lot harder to adjust your run up and the way that you plant your feet (in order to change your hip position) than it is to rotate your upper body and bring your shoulders into line.
The easiest way to rotate your shoulders and upper body is to change the position that you look with respect to your front arm (your left arm if you're a right-handed bowler, and vice versa). Whilst a side-on bowler ought to look, as is traditionally emphasised, behind it (to the left of it for the right hander), a front-on bowler should look in front of the front arm (i.e. between his two arms). This will then bring the shoulders around and drastically reduce the twist in the back. In a large number of cases where a mixed action occurs, it's because a young player has been drilled to look behind the front arm no matter what alignment his hips take. As the explanation above hopefully conveys, this isn't always the case. Taking this to its conclusion for midway actions, the bowler should be looking approximately through his front arm (obviously, this will vary depending on the nature of the action and the degree to which it is removed from either of the two extremes).
Forgetting the biomechanics of alignment for a minute, what other factors are there that can help someone to bowl faster? Well, it's time to return to science, which tells us that we need to increase the force that we place into the delivery to extract extra pace. Two of the simpler ways that can often increase force where it's lacking are to increase the effort placed into both driving the front arm down as you bring the bowling arm up, and doing the same to the back leg (the same side as your bowling arm) as you follow through. The follow-through itself is an area that's often neglected by young bowlers; it should be as long as is needed to naturally slow down without exerting any sudden forces which can both cause injury and reduce the effectiveness of the action (if the follow-through is harsh, it may have to start during the bowling action itself, slowing everything down). The same applies to a run-up, in that it needs to be long enough to allow a bowler to reach the fastest speed where he's comfortable delivering the ball - if it's too short, then the bowler won't bowl as quickly as he potentially could, while an overly-long run-up is just a waste of energy.
Finally, we've got everything sorted out - so how fast do you actually bowl? Naturally, the best thing possible to use would be a radar gun - however they're not generally widely available to clubs and schools - but there is a simple way that needs just a stopwatch and a calculator (or maths geek) to provide approximate results. Start the stopwatch when the ball is released, and then stop it again when either the batsman hits (or misses) it, then divide 45 (or 72) by your answer to get your answer in miles per hour (or kilometres). For example, a delivery timed at 1 second has travelled at about 45mph (72kph). To break the magical 100mph (160kph) barrier, the clock must register at 0.45 seconds. Once you get used to working the timer, you will get surprisingly consistent results. I've found that standing at the back of the net, either directly behind or just to the side, gets the best results.