The combat of Hollabrunn (15-16 November 1805) was a delaying action fought by the Russian that helped prevent Napoleon from trapping Kutuzov's army before it could join up with another Russian army approaching from the north.
In the aftermath of Napoleon's triumph at Ulm (20 October), Kutuzov had been forced to retreat east along the southern side of the Danube. The Russians fought a successful rearguard action at Amstetten (5 November), and were across the Danube by the end of 9 November. The French were temporarily divided by the river, but the Russians failed to take advantage of a chance to crush Mortier's corps (battle of Durnstein, 11 November 1805). After this failure Kutuzov continued his movement to the north-east, towards a second Russian army commanded by General Buxhowden and accompanied by the Tsar.
In the meantime Murat occupied Vienna, and tricked the Austrian defenders of the Tabor Bridge into believing that an armistice had been signed for just long enough to allow his troops to capture the bridge intact.
Napoleon decided to try and trap Kutuzov just to the north-west of Vienna, taking advantage of the intact Tabor Bridge to move Murat and Lannes across the Danube. They would then head for Hollabrunn, hoping to arrive before the Russians. Further west Bernadotte was to cross the Danube at Melk, join up with Mortier who was already on the north bank of the river, and attack Kutuzov from the rear.
The plan failed on both flanks. Bernadotte was delayed at Melk, and didn't cross the Danube until 15 November. Meanwhile Kutuzov had already passed Hollabrunn, leaving Prince Peter Bagration, with a rearguard of around 7,500 men, to hold up the French. Bagration reached Hollabrunn on 15 November. He left an Austrian force under Count Nostitz as an advance guard in Hollabrunn, and then moved the bulk of his forces into a strong defensive position three miles to the north at Schongrabern.
The action at Hollabrunn began with a French attempt at trickery that rather backfired. When Murat arrived at Schongrabern he repeated the trick he had used at Vienna, claiming that an armistice had been agreed between the French and Austrians. He used his unopposed passage over the Danube as proof of his claim. Nostitz fell for the trick and withdrew from Hollabrunn.
Murat then advanced north towards Schongrabern, where he found Bagration. Mistakenly believing that he had found Kutuzov's main force (this was after all what he was attempting to achieve), Murat decided to try and repeat his trick. A messenger was sent to the Russians offering to negotiate an armistice. This time Bagration realised that this was a trick, but decided to take advantage of it. Any prolonged negotiations would give Kutuzov the time he needed to reach the Tsar and Buxhowden, and a second Russian army. Kutuzov agreed to the plan and sent two aides-de-camp to give the negotiations more credibility.
It isn't entirely clear what Murat hoped to achieve at this point. His role was to trap the Russians, allowing Napoleon to surround them. Instead he negotiated an armistice that would have allowed the Russians to leave Austrian territory while the French remained in Moravia. This might have been useful if the Austrians had indeed agreed to an armistice, but it's hard to see how it was meant to help in the actual circumstances. Napoleon was predictably furious when he learnt what Murat had done, and ordered him to break the armistice without the agreed four hours' notice.
Murat's ill-considered trickery cost the French a full day. The fighting at Schongrabern didn't begin until late in the afternoon of 16 November. The French began an artillery bombardment at 4pm, then attacked both Russian flanks. The attack on the right failed, but Lannes had more success on the Russian left, inflicting heavy casualties on two infantry and one cavalry regiment. Despite this setback the Russians managed to hold their ground until evening, when Bagration began a slow retreat. The Russians made another stand two miles further north, at Grund and Guntersdorf, where Bagration found some supporting troops. The fighting finally died down at about midnight. The Russians re-joined the main army, while the French camped around Hollabrunn. Bagration was rewarded for his performance with promotion to lieutenant general.
In terms of casualties the French could claim a victory. They lost around 1,500 men, while the Russians lost 1,479 killed or missing and 931 wounded. In terms of its actual impact the Russians had the advantage, delaying Napoleon's advance long enough to give their main army a lead that he was unable to overcome. Kutuzov was able to join up with the Tsar and Buxhowden, but the combined Austro-Russian army would soon march to defeat at Austerlitz (2 December 1805).