Some more cheats: el ama de casa (the housewife) el asma (asthma) el arca (the ark) el hambre (hunger) el hampa (the underworld) el arpa (the harp) el águila (the eagle) http://spanish.about.com/od/adjectives/a/el_for_la.htm Your point about "el" when referring to people is a good one though. Escpecially when several occupations such as "artista", "dentista", or "modelo" do not change endings for gender, so gender is instead defined by the article.
I guess it comes down to context.
[In 2017] He was the best player in the league - [En 2017] Fue el mejor jugador de la liga.
[When he was young] He was the best player in the league - [Cuando era joven] Era el mejor jugador de la liga.
Out of context the imperfect jumps into my mind too, but either form should be acceptable based on the English.
Yes, "fue" could refer to "he" or "she", but if the gender of the player is known, as it is here, then "jugador/a" must match that gender. If the gender is unknown then "jugador" would be used. So, in a mixed gender league you might ask / answer:
¿Quién fue el mejor jugador de la liga?
[El] Fue el mejor jugador de la liga.
[Ella] Fue el mejor jugadora de la liga.