Hello, I’m a native speaker but not a teacher, that’s my disclaimer. :) The first example “…was playing” can be used in both situations to show both a moment in time as well as through a period of time, but the period of time is known and they are in the past. The thing to remember here is that you’re talking about the past from the PRESENT. What were you doing when I called? I was playing basketball. (The time period is “when I called”) What were you doing between 5 and 8 pm? I was playing basketball. (The time period is 5-8”) What were you doing all night? I was playing basketball. (The time period is “all night”) Now let’s involve Mary and the “had” This “had” is used when telling a story about two points that are BOTH in the past. …had been …had jumped …had [any other verb] In our examples here you’ll be using the word “had” to show that you were doing something in the past when another moment in the past occurred, and you want to make a statement about that second point in the past. So if Mary called you at 8 pm. “I HAD been playing basketball, but Mary called.” Here you are either going to continue talking about Mary or it’s implied that that you’re focusing on that time when Mary called. Either way, you’re in the past at both time points. Basketball is in the past…Mary’s call is in the past. You’re emphasizing that second moment in the past about Mary and that the first activity is over. You could say was “I WAS playing basketball when Mary called,” but in this example you’re not clear that you STOPPED playing when she called. It could be followed with various thoughts: I was playing basketball when Mary called… …so I didn’t hear. …BUT then I stopped. …so she joined the game. …and she wanted to play. “Had” shows you A) stopped playing B) are telling a story about what happened when Mary called (in the past), while you were playing basketball (even further in the past). “Been” makes the activity/verb continuous in the past.