In the context of the Shamatha practice of Settling the Mind if any emotion, for example, anger arises during a meditation session you can become aware of its arising but it’s different than watching a thought, it’s more like your whole experience is suddenly tainted by the emotion, if you then sit still and watch it, you can also become aware of its dissolution.
In the context of the practices of the Applications of Mindfulness and Vipashyana, you can apply inquiry and ask, where is anger located? Where do I feel it, in my belly, in my head, etc? Does it has color, shape, etc? And investigate. By doing this you can gain insight into its empty nature. Also by directing your attention to the emotion instead of the referent which are the thoughts that feed it, in other words, by not following the thoughts that give rise to anger, then the emotion will start dissolving.
When practicing in the context of Ethical Conduct while engaged in activities an interactions with other people, there are several antidotes that can be applied such as not talking, taking space, practicing patience, etc., there are many suggestions from Santideva and other great masters.
When practicing in the context of Dzogchen, you recognize anger as a manifestation of mirrorlike wisdom of primordial consciousness and it self liberates.
The important thing is to practice something, sometimes you will be able to see it arise and without any grasping it will be self-liberated, other times you will be completely dominated but you will still have time to apply an antidote and avoiding letting it transform into hurtful words and actions.
On other occasions you will find yourself regretting what you did or said, but you will still be able to apply a practice of purification.
As the Masters say, using the analogy of a forest catching fire, if you see a sparkle you might be able to stop it by quickly stepping on it, but if the fire is spreading in the forest, you will need to apply stronger measures.
That’s why it’s so important to train in the cushion and be aware of our mental state at all times in between sessions.