Originally playing for the Cockburn Junior Football Club, Sumich represented the Western Australia Under-18 team which won the 1985
Teal Cup. He made his debut for in 1986. As well as playing football, Sumich was also a noted under-age cricketer, playing three
Tests and three
One Day Internationals for the
Australia Under-19 cricket team in 1987 as a
left-arm orthodox spinner. Sumich also attended the
Western Australian Institute of Sport. Sumich was selected by the
West Coast Eagles with a pre-draft selection before the
1988 National Draft. He made his debut for the club in round one of the
1989 VFL season against , recording 10 disposals. After kicking one goal in the first three games, Sumich was dropped back to South Fremantle, but returned in round seven, and played each of the remaining games for West Coast. He finished with 45 goals for the season to be the club's
leading goalkicker, which included four hauls of more than five goals. Against in round 12 he kicked eight goals, setting a record for the
most goals kicked in a match by a West Coast player. In 1991, Sumich kicked 111 goals to finish second in the
Coleman Medal to
Tony Lockett, establishing records as the only West Coast Eagles player to kick more than 100 goals in a season and becoming the first left-footer to kick more than 100 goals. His total of 89
behinds for the season is also a VFL/AFL record. Against Footscray in round 13 he kicked 13.3, surpassing his previous record for most goals in a game (later topped by
Scott Cummings in 2000 with 14.1). He also kicked five goals in West Coast's
Grand Final loss to . Sumich was a member of West Coast's
1992 and
1994 premiership victories over , kicking six goals in the 1992 Grand Final and two goals in the 1994 Grand Final. In Round 18 of the
1996 AFL season, Sumich kicked six goals in a stirring six-point victory over , but was reported by umpire
Greg Scroop for allegedly striking
Damien Hardwick, and was suspended for two matches. Sumich finished his career
in 1997 as West Coast's
all-time leading goalkicker, kicking 514 goals from 150 games at an average of 3.43 goals per game. He also holds the record for the most goals kicked at the
WACA Ground – 101 goals from 29 games. Sumich had been playing on-and-off for South Fremantle since he was recruited by West Coast, mainly when recovering from injury or out of form, but returned to the club full-time
in 1998, serving as co-captain with
Peter Worsfold. He played 17 games for the club in 1998, kicking 25 goals to finish as the club's leading goalkicker, and retired at the end of the season. ==Coaching career==