what’s the meaning of this?

hello, what's the meaning of this?

こんな負けず嫌いがなんで水の中だと競争に興味ないのかなって

and

泳ぐ時もこれくらい本気出してくれよな

?

こんな負けず嫌いがなんで水の中だと競争に興味ないのかなって

I wonder why someone who hates so much to lose is not interested in competition once in water (= when swimming).

泳ぐ時もこれくらい本気出してくれよな

I hope you will exert yourself/be serious like this also when you swim.

Thank you! I ended up figuring out the second one (I'm glad to see it was ok), and somehow the first but I wasn't sure at all...

Thanks again!

The literal translation of 負けず嫌い is indeed "someone who hates to lose," but the phrase is usually used as an equivalent to the English word "competitive." So you can see what the speaker is trying to say here.