The fleet was a large one, with many troops aboard, hence those in the city were frequently unable to prevent their landing at will in places that were less visible or at some distance from the city. On account of this, there were many skirmishes between them, in which it pleased God to allow the Portuguese always to come out the better. Now it happened at this time that Nuno Álvares, who loved to serve the king and was desirous of a good reputation, settled on carrying out a skirmish on his own account, without informing the prior or any of his other brothers. When he saw how those in the naos came out frequently to pick grapes and fruit, because they were in season, he spoke to a noble knight, called Pedro Afonso do Casal, who was married to one of his sisters.

He explained that it was his wish to set an ambush the following day for those of the fleet, should they come out as they usually did, and asked him whether he would like to form part of his company. The other man expressed his willingness. In this way, Nuno Álvares gathered his own men and others together, amounting to twenty-four horsemen and about thirty crossbowmen and foot soldiers.

With this arranged, Nuno Álvares rode out early the next morning and set an ambush at the bridge of Alcântara, below the Monastery of Santos, by Restelo, hiding with his men as best they could among the vineyards and gullies, of which there were many, so as not to be seen from the fleet. As Nuno Álvares was discussing with his men the manner in which they were to encounter the Castilians if they came out, they saw a rowing boat leave the fleet, bearing about twenty men making for the vineyards to pick grapes. When Nuno Álvares and his men saw them, they took good note of where they landed and where they would regroup for their return.

Immediately, his horsemen, accompanied by the crossbowmen and foot soldiers, went to the place where the Castilians were climbing up, which was a deep gully by the vineyards. When they got there, Nuno Álvares and a number of others dismounted and made their way stoutly towards the Castilians.