One of the best ways to beat an opponent is change of pace. The thing I have noticed about most strikers who are untrained, or who have had little of no coaching, is that they get the ball and run hell for leather. This has a number of problems:
1. You reduce the effectiveness of support from team mates.
2. Controlling the ball is harder.
3. Inefficient use of energy.
4. Makes it easier for a defender to tackle or challenge you (obviously if you've got space to penetrate, then go for it at full speed, there are always occasions you can do that).
but most importantly ...
5. At full throttle you can't change direction as easily, your straight line speed is great, but moving your weight off your centre of gravity makes you unbalanced and weak.
6. You have no change of pace, apart from to slow down!
Now, here's what you'll notice with some of the best ball carriers, wingers, players who beat people.
Let's take the left wing position as an example. LM receives the ball and turns asap so he's facing the opposition (see
this post for info). Rather than attack the RB at full speed with the ball (see above points in this post) he'll attack the player but at 60-70% of maximum pace .... then when it comes to the crucial moment, he'll either hit that extra 30% of pace, or combine it with a dummy or skill and thus skin the defender. Sometimes, you'll see them attack at full speed .... ease off ... then burst with speed again, but the effect is the same.
With a LM, really he'd want to get round the outside primarily (assuming there's not an attacking play set up to allow him to cut in), so by 'drifiting' towards the RB, he then adds the extra pace and drives round the outside. For the defender, he always has to react to the ball carrier. How does he react to a change of pace ? He can't but to change his own pace once he reacts to the ball carrier, but remember, he's facing him so that's difficult. He can't change his pace BEFORE the ball carrier does, what's he going to do? Dive in? Run off in another direction? This is why you see RBs and LBs turning side on as if they're facing the wrong way, you think, huh, how's he gonna tackle like that, well, he's encouraging the ball carrier to one side or the other so he can challenge him in a more even contest. Some defenders prefer it, some don't.
'Drifting' towards your opponent also allows you to get that crucial skill right, and scares the crap out of the defender himself, because he knows something is coming but has no idea what. Running at full pelt is easier to tackle for a defender as I mentioned, it's more of an intercepting block because the ball carrier cannot alter direction as drastically.