To say "If you want to play baseball, make sure that it is not raining beforehand" in Japanese, a formal option is 野球をしたいなら、事前に雨が降っていないことを確認してください (Yakyuu o shitai nara, jizen ni ame ga futte inai koto o kakunin shite kudasai), which directly translates to "If you want to play baseball, please confirm beforehand that it is not raining." For a casual tone, you can say 野球をやりたいなら、先に雨が降ってないか確認してね (Yakyuu o yaritai nara, saki ni ame ga futtenai ka kakunin shite ne), meaning "If you want to play baseball, check first whether it’s raining." Both versions emphasize checking the weather to ensure a fun game without interruptions.