Complex sentence: Alves started his professional career at hometown's Varzim SC, playing 15 matches in the Portuguese first division in 1998--99, and subsequently signing with league giants S.L. Benfica; he started representing its B side, appearing 51 times and scoring once.
Split into simpler sentences: Alves started his professional career at hometown's Varzim SC, playing 15 matches in the Portuguese first division in 1998--99, and subsequently signing with league giants S.L. Benfica. He first started playing with its B side, appearing 51 times and scoring once.