There were stragglers in the marathon.
He lost out in the company competition and became a dropout.
落伍者 describes someone who has fallen behind or dropped out of a race or group, whereas 敗者 specifically means the loser of a particular contest.
落伍者 stresses falling behind the group or dropping out, whereas 負け犬 focuses on the shame of having lost a contest or one's social standing.
Standard kanji spelling.
Rare variant; 落伍者 is overwhelmingly more common.
Compound of 落伍 (rakugo, 'dropping out' or 'falling behind') + 者 (sha, 'person'). 落伍 itself is from 落 (raku, 'fall') and 伍 (go, 'group of five' or 'rank'), originally referring to falling out of formation in a military context.