Highest single season SO/9 rates by left-handed starters in Royals history

Play index doesn't differentiate between starting and relief appearances so I set the criteria to players who started in 60% of their appearances with a minimum of 10 starts.

Rk	Player	SO/9	GS	Year	Age	IP
1	Danny Duffy	7.47	11	2011	22	59.0
2	Bill Butler	7.25	29	1969	22	193.2
3	Jose Rosado	6.96	25	1998	23	174.2
4	J.P. Howell	6.69	15	2005	22	72.2
5	Jorge de la Rosa	6.66	10	2006	25	48.2
6	Darrell May	6.51	21	2002	30	131.1
7	Odalis Perez	6.45	12	2006	28	67.0
8	Bruce Chen	6.29	23	2010	33	140.1
9	Jim Rooker	6.14	22	1969	26	158.1
10	Glendon Rusch	6.13	27	1997	22	170.1

Provided by Baseball-Reference.com: View Play Index Tool Used