It is a tough decision to make.

This is true and the most common usage. But it's not just from sports. The person who is "calling the shots". https://english.stackexchange.com/questions/113815/whats-the-origin-of-the-figure-of-speech-call-the-shots "Calling" something is like naming it, it's a word having to do with control and decision and definition. Another phrase you might here is "I'm calling this." which, in context, may mean ending something. So for instance, before a meeting, the boss might say "I'm calling a meeting to talk about the budget", which means calling everyone in for the meeting. But, for instance, if one has been waiting in a meeting too long for another party who never shows, one might say "I'm calling this (off)" which means to end the meeting. The sense is of finalizing the meeting one way or another. This is also used in sports like "The umpire called it for so-and-so." "called it in favor of". So it's like a final naming of the situation.

It is a sports metaphor. Umpires (or referees in some sports) make "calls." They decide whether a ball was in or out, whether a player has done something against the rules, whether or not a penalty needs to be applied. Each of those decisions (or any similar decision) is a "call" Sometimes a call is easy - the ball was nowhere near where it was supposed to go. But sometimes it is hard to make that decision (due to things being very hard to see, or where the rules are complex). That is a "tough call." In casual conversation a "tough call" is that type of decision, one where it is difficult to know and make the correct decision.

Something is very difficult to you while you have to make a decision on your own.