The whole explanation is based on this idea, keep in mind to always manage your risk in any operation.
Several banks could suffer another devaluation of their shares.
BBD could suffer a devaluation of its shares.
There you have it explained, a total of 22 pages of fundamental analysis, the technician could also give you the same idea, use monthly graphs and any tool to your personal taste.
Use any technical analysis, it will also validate the short. I don't need to explain any more reasons. The possibility of making an operation in CALL and selling its devalued shares in the hypothetical case that the economic crisis that several stock investors bet happens. Also, that the risk of loss would be small. Indicate the prices to take into account in a short operation. All the best :).