Rules data comparison: compare node field with a group
Ok, lets assume that your group name is called "Pokemon"

1) Under Conditions, click on Add Condition.

2) In the drop down, select TEXT COMPARISON

3) Click on the Blue Link that says (DATA SELECTORS)

4) Look for your field, if you named it "group", then look for node:field-group

then highlight it, copy and paste it under Data Selector*

7) Under Matching Text put Pokemon

8) click SAVE

Note: obviously, replace Pokemon with your actual group name.