The F Distribution and the F-Ratio · Exercise 12

Players from four different soccer teams are to be tested for mean goals scored per game. The entries in are the goals per game for the different teams.
$$\begin{array}{cccc}\text{Team 1}& \text{Team 2}& \text{Team 3}& \text{Team 4}\\ \text{1}& \text{2}& \text{0}& \text{3}\\ \text{2}& \text{3}& \text{1}& \text{4}\\ \text{0}& \text{2}& \text{1}& \text{4}\\ \text{3}& \text{4}& \text{0}& \text{3}\\ \text{2}& \text{4}& \text{0}& \text{2}\end{array}$$

What is the df for the denominator?

Its source prints no answer for this problem, so there's nothing to check against.

OpenStax, Introductory Business Statistics 2e · §12.3 The F Distribution and the F-Ratio · Exercise 12