This こと simply means "(intangible) thing". Simpler examples are:
悲しいこと sad thing / something sad
嬉しいこと happy thing / something happy
簡単なこと easy thing / something easy
Likewise, 訳の分からないこと means "nonsensical/unreasonable thing", which is the object of the verb 言う.
In case you don't know what this 訳の is doing, you have to analyze this part as a relative ...
My attempts are:
You can use either to mean the same, but I like 1(b) better because 1(a) could mean that, when you were asked, you were reluctant but your friend talked you into playing soccer. Off course, saying 1(b) does not exclude such possibility but at least it sounds more positive to me.