"Down for the count" is an idiomatic expression that means "out of the action" or "incapacitated". If you are looking for some synonyms for this phrase, then you can use expressions like "knocked out", "down and out", "out cold", "done in", "laid low", "downed" or "out of commission". All of these expressions share a common theme of someone or something being down, out, or no longer functional. These synonyms can come in handy when writing or speaking about someone who has been defeated, injured, or otherwise marginalized, and can help to add variety to your vocabulary.