Which sport(s) takes the most endurance?

I'll add tennis to your two.

cycling.

I was going to say NHL - but they get shift breaks - i.e. just like there's breaks in the game for all of the Big 4.

Can't one argue it takes a great deal of endurance to be a giant O-Lineman in the NFL?

not only strength - but a great deal of stamina and endurance playing for 4 quarters giving every ounce of engery to block, pass protect, and impede rushing defenders all while holding your weight on the line attempting to not let anybody get in the backfield.

Basketball in theory, running back and forth up and down the court every play. But there’s so many stoppages for fouls, time outs, and TV breaks that maybe they don’t need all that much endurance.

Cycling isn’t a sport, it’s an activity.

if you walk: golf. esp. mentally.

Of course it takes endurance to be an NFL lineman (and those guys can destroy all of us in running a mile), but they get 40 second breaks after every play, and then get long breaks while the defense is on the field.  According to my scientific google search, the average "active" time over the course of an NFL game is 11-12 minutes of action.  Dividing that in half means the O-lineman are active for 5.5-6 minutes per game.  Of course it's difficult, but hockey players are on the ice, skating around and smashing into each other for 20+ minutes per game.  

Sports use balls (or pucks). That’s why cycling, track, nascar / Indy car things aren’t sports - no balls. Otherwise they’re just activities or exercises.

Don't know which sports takes the most endurance but Test cricket takes a lot. 5 days out in baking sun for 9 hours is too much plus the mental fatigue. May be Hosko or Bob remembers how many pounds did Dean Jones lose in a single Test match in the subcontinent. 

I find watching golf to be very difficult, mentally.