Sorry to hear about your horse. I am not a lawyer, so this is just personal observation and not legal advice. :)
What you do have going for you is quantifiable "damages." If you do lose both breeding and show seasons based on this injury, you can actually calculate a somewhat objective dollar amount for your "loss."
Most lawyers on something like this will work on contingency. In practice, this means that for any decent lawyer the "damages" must be big to be worth their while. Unless you can show a loss of $25k or more, most good lawyers probably will not want to bother. I am guessing this is unlikely unless you are a professional competing at some very high levels.
Some of you other problems are:
- "I can somewhat calculate what happened." In other words you are guessing. That means the BO and their lawyer can also guess, and they are sure to guess differently than you.
- "The B.O. KNOWS I do NOT want halters on" Do you have this as a written agreement? If not, how can you _prove_ this statement? If you can prove it, can you also prove that the BO agreed to this request? Can you also _prove_ that halters in stalls are inherently less safe than no halters? (I also don't like them on in stalls, but I don't think I can prove it is safer).
I could go on, but I think you see my point. Once you go the legal route, it could drag on for months/years and may not come out the way you think.
Try reasoning with the BO. See if they will agree to run it through their insurance. The "friendly" route usually works best, even when you are really mad. Talk it out in a firm but friendly and civil manner and you may get some satisfaction.
Next step could be to play a little hardball and bill them for the vet. Do it in writing. Then tell them they don't have to pay cash - you will deduct the amount owed from your board. :) I did this to my barn several months back (long story). My BO is not that buttoned up, so I got away with it. Before you do something like that you may want to consult a lawyer, especially if you have a written boarding agreement.