RowNumber for group in SSRS 2005

You can easily achieve this with a little bit of vbcode. Go to Report - Properties - code and type something like:

Dim rownumber = 0
Function writeRow()
  rownumber = rownumber + 1
  return rownumber
End Function

Then on your cell, call this function by using =Code.writeRow()

As soon as you start using groups inside the tables, the RowNumber and RunningGroup functions start getting some weird behaviours, thus it's easier to just write a bit of code to do what you want.

You can do this with a RunningValue expression, something like:

=RunningValue(Fields!Team.Value, CountDistinct, "DataSet1")

DataSet1 being the name of the underlying dataset.

Consider the data:

Creating a simple report and comparing the RowNumber and RunningValue approaches shows that RunningValue gives your required results: