Plotting various stats against each other, Radar charts are often used to compare multiple items at a single point.
A radar chart requires one X Axis and one Y Axis data. You can add more than one data to the Y Axis field to create multiple series.
Alternatively, you can select a Group to separate the Y Axis data accordingly.
Please note that the Y Axis needs to contain numeric fields and remember to select an Expression for each numeric Y Axis field by clicking on the field first and then choosing from the drop down. Due to the nature of the chart layout, Radar chart can only be used with absolute numbers (negative values will not show on the corresponding axis).