Don't just look at the Rohirrim; look at the Orcs as well, both at Pelennor and at Helm's Deep. As you can expect from quite a popular film, the charges in LotR have been examined:

• Let's start with this answer from a now-deleted user, where they lay out exactly what you're dealing with during a cavalry charge.
• That answer then gets further examined here by u/PartyMoses, with an examination of the charges in LotR as well;
• And to round things out, u/Iphikrates and u/Iguana_on_a_stick debate a particular facet of cavalry charges here, with historical examination to go with the LotR analysis.