Reddit mentions of The Hussite Wars 1419–36 (Men-at-Arms)

That makes sense. I'm still not sure about how flails would have been deployed though given how difficult it would be to wield them in formation and how vital maintaining formation was to infantry engagements.

My knowledge of the Hussite Wars is pretty limited tbh, hopefully someone more knowledgeable will jump in. If not you could check out this book on the topic. I've not read it but I've read a few of Turnbull's other works and they tend to be well-written and informative introductions to warfare in different time periods.

Theres a whole lot of materials on youtube (and probably on amazon too), just gotta search for the right keywords - Jan Huss / Hussites / Hussite Wars / Czech (or Bohemian) Reformation.

EDIT: Random quick search on amazon for example - https://www.amazon.com/Hussite-Wars-1419-36-Men-at-Arms/dp/1841766658
https://www.amazon.com/Blind-Courage-Unique-Genius-Zizka/dp/B000A0GYGE/ref=pd_sim_14_2?_encoding=UTF8&pd_rd_i=B000A0GYGE&pd_rd_r=JF3DW5958B0GQ7QGZTMV&pd_rd_w=G55U8&pd_rd_wg=kwhx1&psc=1&refRID=JF3DW5958B0GQ7QGZTMV
https://www.amazon.com/WARRIOR-GOD-Zizka-Hussite-Revolution/dp/1848325169/ref=pd_sim_14_1?_encoding=UTF8&pd_rd_i=1848325169&pd_rd_r=JF3DW5958B0GQ7QGZTMV&pd_rd_w=G55U8&pd_rd_wg=kwhx1&psc=1&refRID=JF3DW5958B0GQ7QGZTMV