The Independent Office for Police Conduct (IOPC) investigation is looking at the contact between West Yorkshire Police and 37-year-old Roberto Villa.
Police were called to a disturbance at the Edgerton Hotel on New North Road, Huddersfield, on the morning of December 4 2018.
They arrested Mr Villa, who became ill a short time later and died in hospital.
The IOPC sent investigators to the scene and to the police post incident procedures.
The IOPC is looking at the use of force, by West Yorkshire Police on Mr Villa and the care they provided to him.
Ann IOPC spokesperson said: "Based on the evidence we have analysed so far, including body worn video footage from the officers at the incident, we have served notices of investigation to six West Yorkshire Police officers.
"The inquest into Mr Villa’s death was opened and adjourned on 14 January. With regard to the post mortem examination, the results of further tests are awaited to determine a cause of death."
IOPC regional director Miranda Biddle, said: “Firstly, our thoughts remain with all those affected by this incident. I am pleased with the progress our investigation has made at this stage; the evidence gathered so far has already provided us with a clearer picture of events and we will continue to work hard to establish exactly what happened.
“We have interviewed the six officers under investigation. I would like to make it very clear that our enquiries are ongoing and the serving of notices does not mean that misconduct is proven.”