Frossi is perhaps best known for wearing correctional glasses during his playing years after suffering from myopia from when he was a child. Also, he is known for his developments of the theory of catenaccio, which emphasizes a defensive style of football.
Frossi began his career as a professional footballer with Udinese, and, after a long stay in Serie B (with Padova, Bari and L’Aquila) he was discovered by the coach of the Italian national side, Vittorio Pozzo. Pozzo called him up for the Olympics of 1936. At the Olympics he won the a gold medal and was the tournament top scorer with seven goals. This excited the interest of more well known teams – in the event he was bought by Inter, where he played from 1936 till 1942, winning the “Scudetto” or league championship in 1938 and 1940, and the Italian Cup in 1939.
He was a member of the Italian team, which won the gold medal in the football tournament at the 1936 Summer Olympics.
Shortly after hanging up his boots, Frossi became a coach, and became manager of a series of clubs – Lumezzane, Genoa, Napoli, Monza, Modena and also Internazionale, without however producing any outstanding results. He was the creator of the 5-4-1 line up and is associated (with others) with the development the catenaccio or “lock-out” theory of football. Frossi often declared that “the perfect football match is one which finishes 0-0”, with neither side evidently having made a mistake.
For his short (12 matches) tenure as coach at Internazionale, Frossi did the job jointly with Ferrero, a strong advocate of attacking football. Despite an 11 match unbeaten record, Inter dispensed with his services because of dissatisfaction with his tactical style and it seemed that Ferrero had won the battle of ideas, together with influential players such as Enzo Bearzot. Despite this, it was the defensive footballing theories Frossi, Nereo Rocco and later Helenio Herrera which became dominant in Italian football for the 25 years or so after his time at Inter.
Like many intellectual struggles in Italy, the dispute between advocates of attacking and defensive football continued for years. In international terms, it is probably true that the advocates of a more balanced, attacking football have achieved more success, notably the all-conquering AC Milan team of the early 1990s, managed by Arrigo Sacchi and the 1982 FIFA World Cup winners of Enzo Bearzot.
Frossi was a graduate of engineering. He worked later as a general manager in industry, and then in the last years of his life he was a columnist for Corriere della Sera in Milan.