1. The team usually plays in a 4-4-2 formation. (at a soccer game)

2. two center forwards
(= two strikers)

3. side midfielder (=left midfielder)
two central midfielders
side midfielder (=right midfielder)

4. fullback ( =left back = side back)
two center backs
fullback ( = right back = side back)

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Q1: Is the explanation above is correct?
Q2: Which one is right?
5. full back, fullback, full-back
6. center back, centerback, center-back
7. right back, rightback, right-back

Check out the terminology and the names of the positions here:

http://www.football-bible.com/soccer-info/soccer-positions-explained.html

(I really don't know much about soccer!)

A1: Yes, the explanation provided above is correct.

A2: All three options are correct. "Full back," "fullback," and "full-back" are all commonly used terms to refer to the defensive player positioned on the left or right side of the backline. Similarly, "center back," "centerback," and "center-back" are all acceptable ways to describe the defensive players positioned in the center of the backline. Finally, "right back," "rightback," and "right-back" can all be used to refer to the defensive player positioned on the right side of the backline. These variations in spelling and punctuation do not alter the meaning or usage of the terms.