# [Pyth], 7 bytes

    /1-6.d9

Explanation  

        .d9 # Get the current day of week (0 = Monday, 6 = Sunday)
      -6    # Subtract 6 from the day
    /1      # Divide 1 by the result of the previous operation
            # raising a "ZeroDivisionError" on sundays

[Try it online!][TIO-jc1xgu7p]



[Pyth]: https://github.com/isaacg1/pyth
[TIO-jc1xgu7p]: https://tio.run/##K6gsyfj/X99Q10wvxfL/fwA "Pyth – Try It Online"

###Another 7 bytes solution

    .(U6.d9

[Try it online!][TIO-jc1y0122]

Explanation  

      U6    # Create a list with 6 elements
    .(  .d9 # Try to pop the 7th element on sundays
            # raising "IndexError"


[TIO-jc1y0122]: https://tio.run/##K6gsyfj/X08j1EwvxfL/fwA "Pyth – Try It Online"