with it over the entire course, and that is one of the conditions of a valid race; moreover, whenever the rider has to switch mounts and busy himself with that, he may be overtaken because he is pre-occupied, not because the other horse is faster. The aim is to gauge the horse’s speed over the whole track; if it is left (1) to the final stretch only, the purpose is not achieved.
As for jalab, it is when a man has someone (2) run behind his horse, urging it on and shouting after it to spur it to gallop. This is the explanation given by Malik, and it is the correct view.
Some jurists have interpreted jalab as the rider himself shouting at his own horse during the race and driving it on (3). This interpretation is questionable, for he is not prohibited from striking the animal, nor (4) from goading it with a spur (5) or anything else that encourages it to run; likewise, he is not forbidden to call out to it. This is not unfair, because the other competitor does the same with his mount.
Allah knows best what the Messenger of Allah ﷺ intended by the hadith, and the wording is open (6) to more than one possible meaning.