Here’s a letter describing the battle from a member of the LaCrosse Light Guards, Company B of the 2nd Wisconsin. I don’t have enough detail to include it in the Resources section yet.
Here’s the intro from the LaCrosse (Wisc) Tribune:
Corp. William H. Collins enlisted in the La Crosse Light Guard on April 18, 1861, and served with Co. B until he was discharged as disabled in May 1962. Collins, who later returned to La Crosse and opened a Pearl Street jewelry store, described the battle of Bull Run in a letter to his wife dated July 23, 1861, and reprinted in a 1930 edition of the La Crosse Tribune and Leader-Press.
See the letter here.