There are two things going on in this puzzle. There are four 15-letter answers which contain some squares with circles in them, and then there is the theme, concealed in those answers plus one other.
17A, Feel like quarreling about something – (H)AVEABO(N)(E)(T)OPICK
23A, No halfway effort – (T)OTAL(C)(O)(M)MITMENT
49A, Basis of a false arrest, perhaps – (T)RUMP(E)(D)(U)PCHARGES
61A, Going past the fourth quarter, say – (P)LAYIN(G)(O)(V)ERTIME
Reading down the first letters of each answer, we get HTTP. And further in on each answer, we get, in order, NET, COM, EDU, and GOV. Finally, at 40A, “Letters after two slashes”, we have WWW.