In the battle, a Royalist relieving force under the command of Sir William Widdrington was defeated by the Parliamentarian cavalry of the Earl of Manchester.

Manchester's forces began by besieging King's Lynn in Norfolk with his infantry while the Association's horse rode into the northern part of the county to give a hand to the Fairfaxes.

[5] On 18 September, part of the cavalry in Hull was ferried over to Barton, and the rest under Sir Thomas Fairfax went by sea to Saltfleet a few days later, the whole force joining Oliver Cromwell near Spilsby.

In return, Lord Fairfax, who remained in Hull, received infantry reinforcements and a quantity of ammunition and stores from the Eastern Association.

In response, Newcastle ordered Sir William Widdrington to take a small force of cavalry and dragoons from Lincoln to confront Manchester and relieve the garrison.

Manchester took part of his force and arrayed them on Kirkby Hill to prevent the Bolingbroke garrison from leaving the castle and organizing an attack from the rear.

Cromwell had his horse shot from under him, apparently by Sir Ingram Hopton (who was himself killed in the subsequent fighting and is commemorated by a memorial canvas found above the font in St. Mary's Church, Horncastle).

[8] In Horncastle, at a place now known as "slash hollow", some Royalists were killed or captured when they became trapped against a parish boundary gate that only opened one way (against them) and in their panic the press of men jammed it shut.

For the remainder of the day the Parliamentarians hunted down Royalist stragglers not stopping until dusk, which in October occurs in early evening, when they were recalled by Manchester.