1) Well you have club teams, such as Barcelona/Manchester United/Bayern Munich. These are the equivilant of the Miami Heat/ Boston Celtics/OKC Thunder and such. So a player in an American sport like Dirk Nowitzki, his club team is the Dallas Mavericks, but his national team is Germany. So to put that to whats going on right now in the world of soccer... This is a tournament that happens every 4 years for national teams only. The 2 tourneys that matter most for national team are the world cup, every 4th years, and euro, every 4th year. So every 2 years you get a bigtime tourney.
Club tourneys a way different, teams play their regular season similar to that of ncaa football. Theres no playoffs, each team plays each other twice and the team with the best record at the end of the season is the league champion. Each club league also has domestic tournaments as well, that are happening during the course of the regular season. They mean much less than a league title however. And then theres the uefa champions league, the crown jewel of club tourneys. At the end of each club season, the biggest/best leagues in the world take the top 3 or 4 teams that finished in the standings, of the previous played season, and place them in a tourney that can pit various different teams from different leagues around the world against each other to see whos the best in the world. Example, Bayern Munich of Germany played Chelsea of England in the final this year. Champions League also unfolds as the regular league season is going on for the record...
2) Player loans can happen anywhere in the world, not just to MLS, during the 2 transfer windows during a given season. They take place at the beginning of the season, and in the middle. Teams will loan out players for a couple reasons. First and foremost, the younger players at the monster clubs, who are under contract, will probably not see any time on the field because of how rich the talent is. So instead of just letting them ride the bench all year, they will loan the player out to a lesser team in the world to let him develop his skills and get experience. This also allows the team who has ownership over the player to not pay his salary during this time. So the other reason this happens, is if a player who is getting paid alot isnt playing well, or is too much of a salary hog, the team will loan him out to free up space on the salary wages. Injury is always a concern, but in the case of the younger player being loaned out to develop, its a risk that needs to be taken, or else hell never develop. In the case of the older player being loaned out due to poor performance or money reasons, if he gets hurt, the club that owns him rarely cares... Because theyre not paying his salary, and they will re-load with someone else plain and simple. They loaned the older player out for other reasons, see what i mean?
3) The minute to minute, play by play rules/dimensions to that of the club leagues does not differ at all to that of the 2 big national tourneys ; Euro and World Cup...
Hope this helps... Always trying to recruit/get more people interested in the best sport in the world
