Breakdown of Чем ближе матч, тем больше они тренируются.
они
they
близкий
close, near
чем
than / the (in comparisons)
больше
more (quantity or size) / no longer, anymore
Questions & Answers about Чем ближе матч, тем больше они тренируются.
What is the exact role of чем and тем in this sentence?
They create the proportional comparison 'the [more]..., the [more]...'. Чем pairs with the first comparative ближе to set up the condition, and тем pairs with the second comparative больше to give the result.
Why is there no verb in the first part, Чем ближе матч?
In the present tense, Russian omits the verb 'to be' (is). Even in this comparative structure, you just drop it. It literally reads as 'By what closer the match [is]...'.
Are ближе and больше adjectives or adverbs here?
Russian uses the same simple comparative form for both! Here, ближе (closer) acts as an adjective describing the noun матч, while больше (more) acts as an adverb describing how much they do the verb тренируются (train).
Why does тренируются have a reflexive ending?
The verb тренироваться uses the reflexive -ся ending when people are training or practicing themselves. If you used the non-reflexive тренируют, it would mean they are training someone else.