If you see a leaf on a tomato plant drop after a long period of vigorous photosynthesis and this is followed by physiological decline, you can conclude that auxin stopped antagonizing

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When a leaf drops after a long period of photosynthesis, it is a sign of aging and physiological decline. This is often caused by the cessation of auxin production, which antagonizes the effects of ethylene. Ethylene promotes leaf senescence and abscission, so when auxin levels decrease, ethylene can act unopposed, leading to leaf drop. The other hormones listed (brassinosteroids, phototropin, cytokinin, and gibberellin) do not have direct roles in leaf senescence and abscission.

If You See a Leaf on a Tomato Plant Drop