How to calculate runs above average in sql

hi, am getting sql assessment. i need to calculate the RUNS ABOVE AVERAGE (RAA ) for the given ipl 2016 data from site

i have completed partially. have doubt in further steps,

--select match_id,striker,count(ball_id) from ball_by_ball where striker=339 and match_id=980926 group by match_id, striker order by ball_id

with cte as (select a.match_id,a.over_id,a.ball_id,a.innings_no,b.runs_scored,a.striker,c.match_date from ball_by_ball a join batsman_scored b on
a.match_id=b.match_id and a.over_id=b.over_id and a.ball_id=b.ball_id and a.innings_no=b.innings_no
join match c on a.match_id=c.match_id where c.match_date>='2016-01-01'::date
),cte2 as
(select match_id,sum(runs_scored) as runs,count(ball_id) as balls,striker,(sum(runs_scored)/count(ball_id)) as rpb
from cte group by match_id,striker),cte3 as

(select ,runs- (rpbballs) as strike from cte2 order by strike)

select * from cte3