Speed (or pace) is an important tool in the game of modern soccer, but measuring just what player provides the most isn't as easy as staging a match race.
The figure below shows one way of measuring the top 10 fastest players in MLS, recording the average top speed of a given player when he makes a run (minimum 50 runs recorded). Real Salt Lake's Corey Baird tops the list, followed by Minnesota United fullback Romain Metanire and Inter Miami rookie Robbie Robinson. But there are a lot of potential lurking variables.
For example, in some ways a fullback like Metanire might have an advantage in this kind of measurement, because they are starting their run from a deeper position and have more time to reach top speed. The same could be said of a forward who plays in a system that encourages sitting deep and counterattacking.
Additionally, quality attackers will tell you the true key to separation is not so much speed as change of pace and acceleration, meaning there definitely some players who might have more top-end speed than they typically show on the field, but choose to use it sparingly.
And there's also a matter of match fitness. It's one thing to be the fastest guy once. But if you're not also among the fittest and you're putting in max effort over 90 minutes, your top-end speed is going to decrease as a match wears on, relative to fitter players at least.
It's worth noting that the actual speeds noted here may not be as fast as you think. Take Baird's average top speed of 15.2 mph. If the 24-year-old averaged that speed over a mile-long race, he'd finish that distance in just under 3 minutes and 57 seconds. That's fraction less than 14 seconds slower than the men's world record. And that's a middle distance race, not a short sprint.
As far as true top-end speed? Even your garden variety contestant in a state championship high school meet can run a 100-meter dash runner in 11 seconds or less. That's an average speed of roughly 20.33 mph.
Obviously, many of the best players in MLS are capable of approaching or even surpassing that same speed, were they put on a track and told to run a straightaway as fast as they can. But that's not the kind of data the sport gives us.