With this code but without case sensitive. I want replace all word contain Esports, esports, eSports, ESports etc..
{{ $content := replace $content "Esports" "<a href=\"https://example.com/esports/\" >Esports</a>" 1 }}
You can use replaceRE which does a regex match and then use the i flag to make it case-insensitive.
{{ $content | replaceRE "(?i:esports)" "<a href=\"https://example.com/esports/\" >Esports</a>" }}
You may need to tweak the flags or the regex. This is just the gist. I have not tested it.