I've never seen that film, are you sure you're not talking about Octavian when you say "Julius Caesar?" Caesar never fought Sextus Pompey, only Gnaeus Pompey, and ancient authors generally referred to Octavian simply as "Caesar." Anyway, the de Bello Africo says of Caesar at Thapsus:

Quod postquam Caesar intellexit incitatis militum animis resisti nullo modo posse, signo Felicitatis dato equo admisso in hostem contra principes ire contendit.

Which, after Caesar noticed that it was not at all possible to restrain the roused minds of his soldiers, with the signal 'Good Fortune!' given and letting loose his horse against the enemy he charged against the enemy's front rank

I think this episode is probably what is inspiring the bit in the film, but I haven't seen it so I don't know. Caesar was known for leading attacks personally, though, his total disregard for personal safety is noted not just by himself (and by Pseudo-Caesar, the author of the de Bello Africo) but also by later authors, it was somewhat legendary. At Alesia, Caesar says, he personally led the last of the reserve cohorts to Reginus' and Rebilus' camp, where Labienus was desperately keeping the Gauls from linking up. Caesar claims that his red cloak was seen by his troops, who immediately renewed their attack, pushing the Gauls away from the walls. Plutarch says that Caesar tried to stop the rout at Dyrrachium by grabbing the standards and charging the enemy. Caesar's first military action as a youth was to win the Civic Crown as one of Thermus' officers for leading the assault on Mytilene