Write SQL query to solve given problem: How many simple assaults happened on 2018/9/8?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT SUM(CASE WHEN T2.secondary_description = 'SIMPLE' THEN 1 ELSE 0 END) FROM Crime AS T1 INNER JOIN IUCR AS T2 ON T1.iucr_no = T2.iucr_no WHERE T1.date LIKE '%9/8/2018%' AND T2.primary_description = 'ASSAULT'