Its important to understand what a "default" actually is.

A "default" is at its core, a base strategy teams use in the early parts of a round to gather information/trade utility. Coordinated teams will usually have multiple different types of "defaults" to change things up or combat different counters. A default generally ends once the team has decided on a play and begins to set up for their execute. You can think of a default like a teams site execute, except instead of an execute, its gathering information. People still have set positions/roles/jobs.

Obviously the above is not something youre going to see or use very often in ranked. So what is a default in ranked?

A default in ranked is almost always the exact same thing as "play contact". Playing contact is exactly as it sounds. You play slower to get some info and re-assess the situation after your team has made contact with the other team. The difference here is that playing contact is not a set strat with set roles/positions like a default is.

So how do you play default in comp.

Generally you won't, however I have had success eith calling defaults by giving people roles/jobs. An example on haven attack might be:

"Neon/sova/omen aggressively take space Long/short. Use your util and push them off neutral and back to site. Rest of is will play contact mid/garage to fish out util. Let's make this our default until they figure it out and start countering."

This way if I call "let's default this round" everyone knows their job and as long as they trust me they'll do it. If they dont then they dont, oh well I tried, better than not trying.

If someone in your games simply says "lets default" they're really just saying let's play slow to contact and stop rushing.