was this the "wagon box" fight?  1868?  oh wait, lasz mentioned the haystack fight....coulda been that one.  Both occurred during the combined sioux / cheyenne / arapahoe effort to close a string of US forts being built in thier territory.   They won BTW.  the forts were abandoned, and for a little while their lands were safe.  Red Cloud then went "peaceful" afterwards.
Read "Bury My Heart at Wounded Knee"  for some details.
I believe the numbers were somewhat fanciful, but thats just my opinion.  Red Cloud had some 5000 warriors at his disposal during this war, laying seige to 2 forts and racking up the biggest massacre up until Little Bighorn.  The Fetterman massacre cost the US army 101 men.  I seem to recall a story that a youngster named Crazy Horse was involved in laying the trap.
Anyway....at Adobe Walls, Texas, a fellow with a sharps performed a pretty amazing feat, killing a large number of the attacking comanche at a range of out to 1000 yards.