Allison had a reputation for violence, having survived several one-on-one knife and gunfights (some with lawmen), as well as being implicated in a number of vigilante jail break-ins and lynchings.

On September 22, 1862, Allison re-enlisted, this time in the 9th Tennessee Cavalry Regiment, where he served under the Confederate "Wizard of the Saddle," General Nathan Bedford Forrest.

[citation needed] A popular – possibly apocryphal – story relates that a corporal from the 3rd Illinois Cavalry arrived at the Allison family's farm with the intention to seize it.

After a confrontation and the breaking of his mother's vase (which had been an anniversary present to her from his father), Allison took a rifle from the house and killed the man.

[6] Whatever the reason, Clay Allison, along with his brothers Monroe and John, and sister Mary and her husband (Lewis Coleman), soon moved west.

[citation needed] In the New Mexico towns of Cimarron and Elizabethtown, Allison began to develop a reputation as a dangerous man during the Colfax County War.

In the fall of 1870, a man named Charles Kennedy was being held in the local jail in Elizabethtown, accused of going mad and suspected in the disappearance of several strangers and his own son.

[10] Allegedly, Allison cut off the man's head and carried it in a sack for 29 miles (47 km) to Cimarron, where he placed it on display on a pole in front of the St. James Inn.

[citation needed] At one point on October 31, 1878, Allison was entangled in a small skirmish with Comanches during the ongoing Texas-Indian War in Wheeler County, Texas.

After first racing their horses,[13] Colbert and Allison entered the Clifton House, an inn located in Colfax County, New Mexico, where they sat down together for dinner.

[14] On October 30, 1875, during the Colfax County War, Allison is alleged to have led a lynch-mob to kill Cruz Vega, who was suspected of murdering Reverend F.J. Tolby, a Methodist circuit-rider.

[citation needed] In December 1876, Allison and his brother, John, rode into Las Animas, Colorado, where they stopped at a local saloon.

Constable Charles Faber of Bent County told the Allisons they needed to surrender their pistols, as an ordinance made it illegal to carry weapons inside the town limits.

According to contemporaneous accounts, a cattleman named Dick McNulty and Chalk Beeson (owner of the Long Branch Saloon), convinced Allison and his cowboys to surrender their guns.

Siringo's account relates that it was McNulty and Beeson who ended the incident; He further wrote that Earp had not even approached Clay Allison that day.