I'm working at teasing this out a bit. First off I'm not sure the assumption that the William S Clay listed as a conscript and dying at Rock Island is the same fellow as your relative. A couple of things brings this into doubt. First there is a fellow conscript Eli (Eleazar) Clay listed as dying at Rock Island as well in the same time time frame. This is I believe a gentleman from the Moniteau County Clays. (I'm sure these fellows are cousins of the Willam Spradling Clay from St Francois Co.) Further it appears that both these gentleman belonged to the 5th Missouri Cavalry Co. B, with Eli joining Elliott's Scouts when it was spun out of the 5th late '62.

With that said, we will move on to what I have found about William Spradling Clay to date... Wm S. came from the long and large lineage of Eleaza(o)r Clay who located to St. Francois Co area between 1810 and 1813. Eleazar was a native of Chesterfield Virginia and father to James W. Clay (b 1806) the parent of Wm S. Eleazar and James were a slave owners. The Clay clan obtained a number of land grants in the area of Liberty Township of St. Francois Co. Neighbors include the Bayless (Baliss) and Barnes families (my wife is a direct descendent of both). Also their circle of friends include the Hampton's. Robert D Clay was an uncle of Wm S. That is important in that RD Clay filed a complaint against 3 of Eleazor's slaves in Nov 1863, claiming they had plundered the house and murdered Eleazor after RD found Eleazor dead at home alone. The coroner's report suggests apoplexy as the cause of death and ruled it a natural death though there also may have been a bias against calling it murder and implicating the slaves or Union hands.

See Provost Marshall File:
Clay, David; Clay, Franklin; North, Bale; Clay, John Wesley; Clay, Gabriel: Saint Francois, Farmington: Letter from R. D. Clay offering the whereabouts of 4 negroes he wants to be put into U. S. service. Three of the men he claims were guilty of murdering their 85 year old master, R. D. Clay's father, and plundering the home. 11-04-1863 F1604

This roll is online at http://www.sos.mo.gov/archives/provost/provostPDF.asp

Though I can't say for sure I find it highly plausible that the Clay's of St Francois Co were Southern men in their proclivities. Price did have men in St. Francois Co recruiting before his push including by his own account the infamous Sam Hildebrand who would have been familiar with the Clay's I'm sure. So conscript, recruit, volunteer, I think any of the titles may fit. Question of course remains, if at Pilot Knob, how did he get to Green County? Wounded perhaps and pushed back? Sent towards Arkansas for supplies? Running away?

I guess because of this latter question I find it more plausible that the 5th Regiment guys may have been the fellows in Greene Co because Greene Co was their old stomping ground in '62 and '63 and though part of Shelby's brigade during Price's 64 invasion, they did not actively participate except in the pursuit of the feds after the battle at Pilot Knob.

I'll keep digging....

John R