Shortly after hanging up his boots, Frossi became a coach, and became manager of a series of Italian clubs –
Lumezzane,
Genoa,
Napoli,
Monza,
Torino,
Modena,
Triestina, 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 of the
catenaccio or "lock-out" tactic in football. For his short (12 matches) tenure as coach at
Internazionale, Frossi did the job jointly with manager
Luigi 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 of 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
A.C. Milan team of the late 80's and early 1990s managed by
Arrigo Sacchi, and the
1982 FIFA World Cup winners of
Enzo Bearzot. ==Beyond football==