…I used to run with them, and had great fun; we used to gallop all together round and round the field as hard as we could go. Sometimes we had rather rough play, for they _____ frequently bite and kick as well as gallop.
I googled for the original text and I got the answer that the missing word is "would". But I am not quite convinced of it as the only answer, and I think "might" is also acceptable here grammatically.
What's more, I find the sentence itself not very logical: I don't think "They(they are horses) would frequently bite and kick as well as gallop" can be the reason for "had rather rough play". The horses preferred to play in a violent way because they tended to bite and kick? I can hardly understand the logic here.
Can you help me?