Mars in Sagittarius puts their energy into movement: exercise, travel and outdoor activities. Sports, especially team sports with clear rules, can channel their enthusiasm.
When they take part in a physical activity that interests them, they fill with energy. If it’s a trip, they may organize it with a meticulousness that contrasts with the spontaneity they show at other times.
A broken agreement is a major cause of anger. They may experience a change of rules as a lack of respect, even when the other person has good reasons to change them. They find it hard to accept that a commitment may need revising.
The image of the rearing horse expresses the intensity of that reaction. Firmness and affection help mark a limit without falling into the same agitation. Appealing to their sense of justice (“Do you think that’s fair?”) can invite them to consider their partner’s perspective too.