Barnsley

Coatsworth made his Football League debut on 19 December 1987 at home to Millwall.^[1] His team were 2–0 up when his "sloppy pass-back" allowed the visitors' Teddy Sheringham to score, but Barnsley went on to win 4–1.^[6] He did not return to the first team until the last few matches of the season, when he made three appearances as a substitute and two starts, but he played only reserve-team football in 1988–89 and was released at the end of the season.^[1][4]

Darlington

Coatsworth signed for Darlington, newly relegated to the Conference but managed by the ambitious Brian Little.^[4] Initially unable to displace Les McJannet from the right-back position, Coatsworth finally made his debut in November 1989; he broke a collarbone and was out for six weeks.^[7] By the last match of the season, away to Welling United, Darlington needed a draw to ensure promotion back to the Football League, whatever result was achieved by rivals Barnet. They had injury problems in defence, so Coatsworth came into the side and, with four minutes left and the match still goalless, he met a free kick with a header that looped over the goalkeeper and secured a 1–0 win.^[8][7] At a 2003 event held to mark the club's leaving their long-time home, Feethams, the award for the club's most important goal went to Coatsworth, for "the winner at Welling that took Quakers back into the Football League".^[9]

He began the new Fourth Division season as a reserve, starting twice in October when both McJannet and David Corner were unavailable and a further twice in similar circumstances in December; he scored his first Football League goal on 1 December with a powerful header in a 3–1 defeat away to Stockport County.^[10][11] The last of his 12 league appearances was in the final match of the campaign, from which Darlington needed and achieved a win against Rochdale to secure a second successive title.^[12] Little left for Leicester City in May 1991 and,^[4] after finally becoming a regular in Darlington's starting eleven,^[13] Coatsworth followed him to the Second Division club in October for a £15,000 fee.^[14]

Leicester City

He made his first league start on 30 November in a 2–1 win away to Derby County, and performed well enough to keep his place for the next match,^[15] during which he was substituted with what was reported as a jarred knee.^[16] Minor surgery and specialist rehabilitation failed to fix the problem,^[17] and a second operation – nearly three months after the original injury – confirmed a ruptured cruciate ligament.^[4] It was another year before he returned to the first team, but his return marked the start of a winning run that included his first goals for Leicester – a header and a "superb angled drive" with three minutes left to complete a 3–2 win away to his former club, Barnsley^[18] – and pushed the team into the play-off positions for a second year. Also for a second year, Coatsworth was unfit for the play-off final, having put a premature end to his season by playing on an already injured ankle.^[4]

He signed a two-year contract in July 1993,^[19] injured a hamstring in pre-season,^[20] and his only appearance in the first few months of the new season was as a substitute in the Anglo-Italian Cup in September.^[1] He came into the side in December, and for the first time in his Leicester career, was able to retain a regular place. His 25-yard (23 m) volley opened the scoring in a 2–1 defeat of Luton Town that helped Leicester reach the play-offs for a third consecutive year and, according to the club's website in 2020, "remains a point in time for Foxes supporters".^[4][21] He scored again in the last regular-season match, a draw with Wolverhampton Wanderers, and according to the Leicester Mercury was the most influential player on the field.^[22] In the final, opponents Derby County took the lead "when, with four minutes left before the break, Gary Coatsworth inelegantly thumped a high ball into the middle it soon became the sweetest pass hit by a City player this season."^[23] The referee missed Iwan Roberts' foul on Derby's goalkeeper, while the covering defender missed Steve Walsh's weak header on the goal-line and the scores were tied. Walsh scored again late in the game, and Leicester were promoted to the Premier League.^[24]

Coatsworth was not included among the players named by Little as those he expected to use in the opening weeks of the 1994–95 Premier League season.^[25] He continued for a few months in the reserves,^[26] until, in February 1995, he confirmed his retirement from professional football.^[27] Because of the club's injury problems at the end of the previous season, Coatsworth had played on despite a cyst that caused severe swelling in his ankle after a game. Removal did not fix the problem, and a surgeon told him that he had arthritis which would lead to serious mobility issues in later life if he continued to play professional football.^[27][7]