How do you say '' will win '' in spanish?

You can say "Ellos jugaban". This can be interpreted as "they played", but by using the imperfect tense, it implies action in the past over a period of time, and usually means "were playing" or "used to play". If the preterit is used, "ellos jugaron", that would imply action in the past occurring at a specific point in time, "they played".

If 'they' were females, 'Ellas' instead of 'ellos'; but if the context is clear, no need to use either: 'Jugaban' would suffice.