The primary responsibility of a defender in the game of football is to defend his team's citadel, or in other words, to prevent the other team from scoring.However, throughout the game's storied history, there have been a number of defenders who have ventured upfield with aplomb to score goals for their teams. In the process, they have added an extra dimension to their teams' attacks. Top ten goal-scoring defenders in the 21st centuryIt is always beneficial for a team to have goal-scoring defenders in its roster, during open play as well as in set-piece situations.On that note, let us have a look at the ten-most prolific goal-scoring defenders - retired or active - since the turn of the century.#10 Andreas Holzl - 52 goalsAndreas HolzlAfter commencing his professional career with FC Wacker Innsbruck in the Austrian second division in 2003-04, Andreas Holzl has gone on to make his name as a goal-scoring defender in the country's club football.The 35-year-old right-back has scored most of his goals - 35 of 52 - during a productive six-season stint at first-division Sturm Graz, with an impressive 12 of them coming in his first season at the club.#9 Marc Dal HendeMarc Dal HendeAfter debuting with Vyborg in 2009, Marc Dal Hende has played for five more clubs in the Danish first division.The goal-scoring left-back has scored goals in all but two seasons of his club career. Hende has enjoyed the most prolific spell of his career with Midtjylland, scoring an impressive 22 goals in four successful seasons at the club.#8 Philippe Clement - 53 goalsPhilippe ClementBarring a lone season at Premier League club Coventry City, Philippe Clement spent 15 seasons of his playing career in the Belgian League.The centre-back, who debuted for Genk, prospered at Club Brugge during a decade-long stint at the club. Clement scored 50 of his 52 goals for the club while winning two Belgian league titles and other domestic honours.Today is a special day! Philippe Clement celebrates his 50th game as our head coach against his ex-team. Let’s go! 👊🏼 #CLUBEE pic.twitter.com/q9nhsQUhhb— Club Brugge KV (@ClubBrugge) August 23, 2020Clement, who is now the manager of Club Brugge, won the 2019-20 league title at the club.#7 Dani Alves - 58 goalsDani AlvesOne of the finest goal-scoring full-backs in the modern era, Dani Alves plied his trade at three different top-5 league clubs in Europe.However, it was in Barcelona where the marauding right-back made his name. During a highly successful eight-season stay at the Camp Nou, Alves netted 21 goals and provided a whopping 101 assists.937 - Dani Alves is the player with the most tackles won in LaLiga since, at least, the 2005/06 season (937). Intense. pic.twitter.com/qx6lgYa0v0— OptaJose (@OptaJose) May 7, 2020The 37-year-old Brazilian won a staggering 20 titles at the club - a tally that comprised of six La Liga titles and three Champions League honours.Alves later went to play for Juventus and Paris St. Germain before returning to his native Brazil in 2018, and now plies his trade with Sao Paulo.