It doesn't matter what Gregg's ERA was. Your team ERA is figured by taking the total ERs your team allowed divided by total IPs your team had multiplied times 9 (9 innings in a game). So say before Gregg, your team had 9 ERs allowed in 36 IPs - ERA 9/36x9 = 2.25. Then after Gregg's implosion (4 ER w/ 0 IP) your ERA = 13/36x9 = 3.25. Technically, Gregg cannot have an ERA if he didn't record an out, but your team can still have an ERA.