The date would have been on or near, March 31st, 1862.
The 21st Tenn was commanded by Colonel Edward Pickett with 616 men.
The Union forces were under the command of Colonel Buford (who use to command the 27th Illinois Regiment).
The 15th Wisconsin Regiment, under Colonel Heg, 2 companies of the 2nd Illinois Cavalry, plus Captain Hutchen's company of cavalry. Capt. Sarrestrom's battery of Four-6 Pounders. The 22nd Missouri (4 co's) were the reserve.
Also the Gunboat, "Louisville" was working along with the mission.
On OR 8, page 124, confirms, that "Col Buford, routed the enemy and captured 4 flags."
Colonel Buford reported "3 Large Flags, 2 Guidon's".
The battle was not "in" Union City, but just a bit away.
I hope that helps, I am just reading page for page on the OR'S. Ran as many searchwords as possible, now just going to read the whole thing and see what comes up.
Gregg, great article in the Blue&Grey magazine. That man, Frank O'Reilly, did the colorful, regimental detailed maps on Fredericksburg, Chancellorsville, Spotsylvania and the Wilderness. His book is very good on Fredericksburg, but I don't believe he is a expert on the flags. He is the leading expert on the battle of Fredericksburg. But I am going to agree with you that the flag in question was not the 19th Georgia but indeed the 14th Tennessee.
They had me confused in OR 8, I thought at first it was at/in/near Island Number 10 or New Madrid. This turned out to be out in Western Tenn.
I hope that helps, make sure to check out, OR 8, page 124, for Buford confirmation on capturing the flags. But what flags? Were they all from the 21st Tenn or all from the CSA Cav regiment?
Have a good day, Gregg
Shawn Prouty