If he received pen time or a straight probation in his prior felony possession of a controlled substance case, he is no longer eligible for probation. If he is convicted in a trial in this new AADW, neither the jury nor the judge can consider a probation. However, the prosecutor can offer probation if a plea agreement is reached without a trial. Seek an attorney well versed in criminal law, especially one familiar with the Travis County district courts.
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Ms. Haines' answer is right on point. One thing I'd add, though, is to keep in mind that the prosecutor isn't the only one involved with this--the judge has to approve this or any other plea-bargain agreement. Usually, that's not that big a deal, but some judges are more proactive with that process than others.
Also, as you asked in your follow-up question, yes, deferred adjudication would be a legal possibility here, but I don't think you should hold your breath on that one. Deferred adjudication is intended to give defendants who have screwed up once a chance to get their lives back together without having a conviction that might derail their chances of being able to do that. If you've already got a felony conviction, that logic doesn't really apply.
A person is authorized to use deadly force if they are facing the use of deadly force. Being physically confronted by 3 people might be deadly force. So it is possible that a person in this situation has a defense to the aggravated assault charge.
This is the kind of factor that a good criminal defense attorney can use to the client's advantage and possibly work out a deal for probation in a situation where at first blush it wouldn't seem likely.
Especially in Travis county where the prosecutors and judges are more reasonable than in other places, probation may well be an option if the facts of the case are right.