It would measure the distance and it may even record some top speed during sprinting, but it may get quite confused because of constant direction and velocity changes and eventually the signal can be lost. That’s at least my experience when using it on the track (when doing tempo 100’s) and when trying to measure some speed work with it.
If you’re looking for more “precise” speed measurements (I believe it’s more precise with the shorter distances and sudden direction changes) you should probably consider using a foot speed sensor (not sure if really applicable in soccer)
sth like this for example: http://compare.ebay.com/like/220749588711?ltyp=AllFixedPriceItemTypes&var=sbar