The following is a scenario for the popular skirmish rules in the black powder era Sharp Practice published by TooFatlardies in the context of the Salamanca campaign in 1812 won by Wellington's allied forces.
Before the actual battle of Salamanca (or “de los Arapiles” as it is known in Spain) was fought, on 21st of July 1812 the British and the French armies spent several weeks following closely each other looking to exploit a moment of tactical advantage to defeat the enemy in force.
Since the end of June 1812, the theatre of operations had moved north of Salamanca, to the Duoro river line where both armies try to outmanoeuvre the enemy during several weeks.
Marshall Marmont finally caught Wellington out of step in a faint move in which the French crossed to the southern bank of the river, posing a flanking threat to Wellington and also potentially cutting the line of retreat to Salamanca and further afiled, to Portugal.
On July 17th, Wellington ordered the army retreat towards Toro; the objective was to move from there via the north-south road that links this city with Salamanca. The retreat continued during the 18th reaching by mid-afternoon the line of the Guareña stream, a small tributary of the Duoro. The British crossed this small river unopposed and formed a line along the west bank, supported on the village of Vallesa on the right.
Considering the position sufficiently secured and the late hour (around 4PM), the British were ordered to prepare the camp for the night.
However the French thought differently and spotted a good opportunity to cross the Guareña at a lightly defended position on the left of Wellington’s line. This move if correctly executed will allow a flank attack on the British and allied forces.