How to identify subject verb agreement in a sentence?

Hi!  The change in verb form in those sentences is about how we perceive the collective noun "team." 

"The team is playing well". Here, "team" is seen as a single entity, so we use the singular verb "is." This implies the team is functioning as one unit.  While "The team are arguing", in this sentence, "team" is viewed as a collection of individual members, which is why we use the plural verb "are." This suggests the members are acting independently of each other. 

It depends on whether you want to emphasize the unity of the group (singular) or the individuality of its members (plural).  In American English, collective nouns are typically treated as singular, while in British English, they can be plural when focusing on the individuals. 

Hope this helps!