In New Mexico, the crime of battery is defined as the following:
30-3-4. Battery.
Battery is the unlawful, intentional touching or application of force to the person of another, when done in a rude, insolent or angry manner.
Whoever commits battery is guilty of a petty misdemeanor.
And the crime of assault is defined as follows:
30-3-1. Assault.
Assault consists of either:
A. an attempt to commit a battery upon the person of another;
B. any unlawful act, threat or menacing conduct which causes another person to reasonably believe that he is in danger of receiving an immediate battery; or
C. the use of insulting language toward another impugning his honor, delicacy or reputation.
Whoever commits assault is guilty of a petty misdemeanor.
As you can see from those statutes, for an assault in New Mexico you do not have to make contact with the other person. Thus, throwing those keys would be assault if it was an attempted battery (i.e. the attempted unlawful, intentional touching or application of force to the person of another, when done in a rude, insolent or angry manner) or if it was an unlawful act, threat or menacing conduct which causes another person to reasonably believe that he is in danger of receiving an immediate battery. What this means is that perception of how you threw those keys matters a lot. You have admitted you were angry at the scene of the repo. That anger may have shown through when you tossed the keys. If what the officer and the repo guy saw was an attempt to throw the keys to hit the repo man then the cop was justified in thinking it was an assault. That would meet the necessary probable cause for the arrest as probable cause is a pretty low standard. Your perception of the incident is obviously different from what the cop will say occurred. So if it goes to trial, the issue for the jury will be what really happened when you tossed those keys. Unless there is video of it it’ll come down to what the various witnesses say when they testify and then the jury will have to choose what to believe. So I don’t see this as quite the slam dunk in your favor that perhaps you think it is.
Even if the arrest for the assault wasn’t good, there was a warrant for your arrest and the officer was certainly entitled to arrest you for that. Given that, I don’t see a good false arrest case for you here even if you get the assault charge dismissed. But you might want to run that by a civil litigation attorney for advice on that. Your more immediate concern, though, is the assault charge and I would strongly recommend you get a lawyer to defend you on that.

