My understanding of how tenure-denial appeals work is limited, but growing by the day, unfortunately. Perhaps the process varies (a lot?) from institution to institution, but here are some things I have learned so far:
The basis for a realistic appeal can be (1) discrimination, or (2) violation of procedure. An appeal based on an "I was misjudged" is less likely to be successful, although I know of some cases in which an appeal of this sort was successful, typically based on the issue of the relative weights given to teaching and research excellence.
Even if there has been blatant discrimination or a violation of procedure, the various stops along the tenure trail designed to catch such things may not catch them, or may even be the source of the problem. Hence the appeal process.
Things can get complicated at large institutions in which there are many intermediate steps along the road to tenure during the evaluation and voting process. At each stage, there is the possibility of a decision that is different from preceding ones, although this gets less likely as the process moves up the administrative food chain.
Nevertheless, voting and decision-making bodies/people at a university can include
- a departmental promotion & tenure committee,
- tenured faculty in the department (perhaps in more than one department for interdisciplinary faculty with multiple tenure homes),
- the department head,
- a committee at the college level (e.g., College of Arts & Sciences, School of Engineering),
- the Dean (± an Associate/Assistant Dean),
- various Provostial Beings ± Vice-Presidents for Whatever,
- the President/Chancellor, and, in some cases,
- a Board of Trustees.
If all of these people/committees vote overwhelmingly no, that's not good (and makes an appeal very unlikely to succeed), but what if some say yes and some say no, or what if there are mixed votes in certain committees?
According to legend, once you get past the department and college/school committee with a positive vote, you're fine, but there are rumors of candidates who had positive votes up to the Dean or Provost or President and then.. zap. There are also sad stories of people with majority positive votes at various stages but not a supermajority of positive votes, leading to cascades of negative votes at later stages of the process.
The appeal process appears to be highly structured (= bureaucratic), with lots of steps and lawyers and invocation of an institution's "tenure code" or criteria by both sides.
If the process leading up to the tenure evaluation works as it should, the results of the tenure evaluation itself should not be a big surprise. There can be a discrepancy between what a department/institution thinks of a candidate vs. what is expressed in the external letters, but even this should be evident in advance if the pre-tenure evaluation process works as it should.
Whether evaluation of probationary faculty is at one intermediate time (e.g., 3rd year) or every year, there should (ideally) be a paper trail that documents how an assistant professor is doing in terms of the various job components, with specific suggestions for improvement if there is a problem, and additional assistance/mentoring given where needed.
Having a well-functioning, fair, and informative system is essential to the tenure-track faculty member and to the rest of the institution. When that system breaks down, owing to incompetence, indifference, or malevolence, and the tenure decision is negative, the grounds for an appeal are laid.