West Midlands Police (WMP) responded to reports of suspicious activity on The Green, Kings Norton, at around 1.40am on Christmas Day (25 December).
Following a brief foot chase a man was detained but he became unwell and was taken to hospital. He died a short time later.
A post mortem will take place on Monday (27 December) to establish the cause of death.
A spokesperson WMP said: “Our Professional Standards Department (PSD) have been informed, as is standard procedure.
“We’ve also contacted the Independent Office for Police Conduct (IOPC), again as standard procedure in such circumstances.”
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