I think the center of my defense would be disproportionate punishment for similar offenses. It's easy and obvious in this case. It also is a core and fundamental reasoon why the arbitration process exists -- to ensure evenhandedness. With respect to the nonsense about cell phones and what the texts show or whatever, my front line argument would be that the NFL invented these "violations" by treating this alleged violation different from similar ones. If the NFL had ordered a five million dollar investigation, demanded Cam Newton's cell phone, conducted 4 interviews of the Panthers' ball boy, etc., they surely would have encountered similar events.
I would also want to get into the merits of the case against Brady, but how you do this is delicate. Judges do not like to make assumptions about bad motives unless the evidence is compelling. You have to be careful about how you pitch these arguments. You want the judge to conclude on her own that there was bad faith, without arguing it directly. You want the judge to get there on her own, because if she does she will be in your corner forever.
So, how would I pitch it? May argument would go something like this. A question that needs to be answered is why was the punishment here so disproportionate. There are two fundamental reasons. First, the league has become wildly successful -- the most successful in American sports -- by embracing an unwavering commitment to parity. It has discovered that giving every team hope keeps fans engaged and also allows them to sell games involving all its clubs on Thursday nights, Sunday night etc. the draft, the salary cap, the scheduling rules all reinforce this approach. The Patriots have, quite famously, resisted these efforts. They draft low, lose players from the salary cap, and play a hard schedule every year, but have sustained excellence. This has caused animosity in the league along with a "they must be cheating" sour grapes environment. I would support this with media reports and also take Spygate head on to show how different perception was from reality. Second, I would focus on the immediate aftermath of the Kravitz story and the Mort tweet. Even though they got the facts wrong, these events led to a media and firestorm unmatched in the history of sports. It hit a public culture nerve, and extravagent pronouncements of guilt were declared on nation news on scant evidence later shown incorrect.
It was in this environment that the league conducted its investigation and issued its decision. And, unfortunately the league fell right into the trap created by the two factors mentioned above. It asked its investigator not only to find and present facts, but then to give an opion about what the facts "probably" meant. Then, the league used that one man's opinion to set punishment. That was a serious error, and the environment in which the exercise was conducted led to inordinate pressure to reach that opinion. But no one man's opinion is more valuable than any other's. And as it turns out, one can take all the very same facts in the report and reasonably conclude it was more probable than not that Brady did not have a general awareness of a probable violation. Indeed one could take all the facts in the report and reasonably conclude it cannot be said the preponderance of the evidence supports a finding of any violation at all.
Then, and only then, would I set out the report's deficiencies. In short, I think how this is presented is critically important, and one needs a very clear outline to explain why each issue is relevant without directly attacking motives.
This approach also has the advantage that, taking out hyperbole and trying to be as neutral as I can as a Pats fan, it is close to what I think actually is the truth.